My perspective (as a former 60mm 11C Section Leader w/ 2/75 Rangers & later 11CS/18B SF Heavy Weapons NCO);
1. The baby mortars (50mm -60mm) are a very responsive and effective form of firepower. Quicker to employ than distant supporting fires. In that respect, no different than GPMGs, AT launchers, or manpack recoilless rifles. Some systems (like the M19 & M224 I used) are very capable when laid-in for observed fire missions. Just as accurate and adjustable as their bigger brothers, but operating within the lesser range limits of 60mm ammo.
2. 60mm ammo is simply much more effective than rifle launched grenades. More explosive payload, more range, more fragmentation, greater burst radius, greater lethality. And most importantly... more effective options to throw against the enemy: HE, WP, or Illum. Proximity (4m high air burst), near surface (1m low air burst), impact (point detonating), & delay (.5 second to penetrate overhead cover) fuzing. Tailored effect that grenade launchers and most AT rockets just can't match. Enemy PKM at 1000m over on the next hill? They'd better have overhead cover. Or be able to shoot through a cloud of WP while they're also on fire. Enemy squad maneuvering up a wadi or arroyo while out of direct line of sight from most friendly weapons and observers? Air burst. Indirect fire. The ability to reach directly over or behind protective terrain. Area effect.
3. Handheld mode is something that varies in effectiveness depending upon one thing: live fire training expenditure. In units where gunners get a lot of live fire practice ammo, handheld fire is amazingly effective. If gunners only get rare live fire practice in that mode, less so. Pretty much the same constraint that determines a grenadier's effectiveness with his grenade launcher. If you fire enough ammo often enough, the ability to smoke point targets with initial rounds goes up exponentially. If I give a 40mm grenadier an afternoon and a case or two of ammo, I can have him placing 40mm grenades directly through pickup truck side windows at 250 meters by the end of the day. So it is with handheld mortars. Live fire practice makes perfect.
4. But... mortars in effect deliver area munitions. Precision hits are great, but not usually necessary. An air burst gets everything not under cover within its effective radius. Denying the use of reverse slope defenses and open to the sky positions. Illumination flares (especially invisible IR rounds) disrupt the enemy's night time Cloaking Device and gets followed by effective fires. WP both obscures the enemy's ability to observe you and effectively train his fires on you. Sowing confusion & uncertainty. Allowing you to maneuver forward (or withdraw). It also burns shit. Most people have a visceral aversion to being burned alive. Mortars deliver not just physically lethal effect, but also psychological effect. "My bullet defeating cover isn't working, I can't see the other guy, I have wounded & dead, and my men are on fire...!" Kinda like the threat of the bayonet... but at distance. Something that causes the enemy to waver where he might otherwise stand.
5. At 2/75, I began as a 60mm assistant ammo bearer (load bearing donkey with a rifle), progressed to gunner (load bearing donkey with a cannon & pistol) and eventually became the mortar section leader (load bearing donkey with manpack radios & rifle). We fired more annual live rounds as a 2-gun company mortar section than a mechanized brigade's complement of mortars for the time. It showed. We could jump in, get the section "Into Action" (laid in) within minutes, and provide accurate & responsive indirect fires called in by Line Doggie FOs or Company FIST.
But... in travelling mode we employed that little puddle shooter by having the gunner wearing it slung across his front with a ready round handy. Already set in trigger-fire mode. Essentially employed as a big trigger fired grenade launcher. With a WP round as the first shot. That choice being predicated on the idea that it was useful to kill, burn, & obscure the first visible (or directed) enemy target. In the event of a TIC, that flaming white smoke would suppress the enemy, obscure his fires, and give the company's other weapons a target indicator for engagement. Usually travelling a ways back in platoon or company movement formation, the gunners naturally awaited calls for fire from Platoon or Company Leadership, who usually kept the mortars in their hip pocket. But in the absence of immediate guidance, the gunner was expected to start looking for business just as a machine gun team or grenadier would.
6. Direct Fire Mode. That little bit in the video where the guy fires his small baseplate against a vehicle tire? Sorry, that's sales fluff. He didn't hit anything he was remotely aiming at. He barely kept the gun from bouncing into his leg. Not only would I not do that to a perfectly good tire sidewall on the vehicle I'm depending upon, but the accuracy isn't there for anything but Saving Private Ryan Sticky Bomb distance. Which is too fucking close for a mortar round. On even the most minimum charge, a recoiling "handheld" mortar will chop your toes right out of your boots if you somehow got them under the baseplate. Never mind "knee mortars" (which never were designed for firing off of a knee).
In my younger days, we experimented with 60mm M19s as Direct Fire weapons. The concept worked... somewhat.
Most effective was to shoulder mount the tube like a Gustav or LAW, and snug the small baseplate into a tree trunk or sandbag. (You need something with a little bit of give or you run the likely risk of cracking the baseplate in half.) Then press the firing lever while using Kentucky Windage over the top of the muzzle. You had to be aware of arming distance.
Most likely and practical use is to engage windows or doorways on building or bunkers, followed by moving vehicles. The round has to stay snugly seated at the base of the cannon's interior base, so you're pretty much limited to keeping the muzzle just above horizontal. Improvised bazooka with no sights. We also tried direct fire off of bipod mounted guns. The problem was that at maximum feet forward extension of the bipod, with the gun pointed more horizontally than vertically, all the recoil tended to kick the baseplate rearward rather than downward into absorbent Mother Earth. Meaning that at the moment of firing, the cannon's recoil drove the baseplate straight back across the ground, the bipod legs collapse and tip to one side, the cannon depresses to slightly below horizontal... and the round shoots out of the muzzle and slithers like a live explosive snake through the grass immediately in front of the gun... armed but not detonated. It always helps when you have someone like 2nd Ranger Battalion Commander LTC Wayne A. Downing watching the demonstration. LOL.
But yeah, with a handheld 10lb mortar and small baseplate, you could launch rounds into a 2nd story window across the street, or even into a bunker face... as long as you could find a recoil absorbing surface to take the blow of the base plate's impact. You are not holding the cannon in your hands and firing it. Mortars are designed to shoot up into the sky and send all recoil down into the ground. "Handheld" means that the meat puppet shooting it uses his hands to hold the thing pointed up, aim it, and keep it from falling over. He doesn't do a thing to absorb recoil by use of muscle power.
In Afghanistan we sometimes kept an M224 cannon & small baseplate strapped to the cargo bed roll bars in Toyota pickups and placed a couple of sandbags on the cargo bed floor. No bipod, no sight, and no large baseplate. In theory, we could fire from the bed. In reality, any engagement where we continued to move meant that everyone in back was either manning the pintle mounted machine gun or holding on for dear life. But it was a simple thing to dismount, unstrap the cannon, and access three or four boxes of vehicle carried 60mm ammo when stopped. The ammo crates made handy cargo bed seats for anyone in back.
Which leads into the whole notion of bringing along handheld mortars for motorized troops. If you're in an RG/MRAP/SUV/Pickup type vehicle... why the hell not? With wheeled transport, you can carry a significant & fight deciding amount of mortar ammo. Vehicle carry solves the number one problem with humping mortars... ammo supply.
7. Organization & Manning for a Handheld Mortar. During my time in Army SF, I had occasion to mount the occasional training mission where we used 60mm M19 cannon tubes to support DA Missions. Strap the gun to a ruck, load everyone with ammo for that specific mission's Actions On the Objective, and carry on with infil. Like the guy in the video with the Gucci carry bag for the 10lb cannon. Great for SOF. Raid type support weapon. Operator also carries a carbine. But in an Infantry platoon or company, guns need to be organized as teams... just as you would with an M240. One guy cannot carry a useful amount of fire mission ammo, plus an M4A1, plus the mortar tube, plus all his other stuff. One guy can carry and employ a little commando mortar, but he isn't able to sustain fire, nor provide his own local security (while firing) without at least an assistant.
I'd disagree with incorporating handheld mortars at squad level as a general MTOE practice. Especially in a typically wartime undermanned US Army 8-man squad. But... at platoon level, you simply assign a 2-3 man mortar team same-same as your organic or attached GPMG or AT teams. Which is how we did it in the Ranger Batts. They can carry a moderately useful load of ammo (since they aren't carrying bipod, sight, large baseplate, plotting board, aiming stakes, aiming stake lights, firing tables, accessory batteries, etc.). Instead, the gunner has that big trigger fired cannon, the assistant gunner is available to load, and the ammo bearer (if present) provides ammo prep & rear/flank security while the gun is in action. All three carry rounds. All three carry carbines. Everyone else in the platoon carries 2 mortar rounds. Except for machine gun or AT crews, RTOs, and medics.
Mortar crews have their own MOS and section organization at MTOE unit levels. Because the weapon system & skill required is pretty involved. You have to grow Gunners, Fire Direction Control specialists, Mortar Section Leaders over many months and years. Because you are throwing HE artillery rounds at targets unseen by the firers. Laying in guns on magnetic azimuths, calls for fire, forward observer procedures, coordinated illumination missions, firing sheafs, TOT missions, screening missions, plotting boards, FDC computations, reciprocal lay, traversing fires, and all the other voodoo involved. You can only train folks proficiently to those skills by centrally manning a dedicated mortar section or platoon.
With handheld fires, you reduce the training requirements to very simple Direct Lay or Direct Alignment missions (visual direct fire targeting). Really no different than how you employ grenadiers or machine gun teams. See the target, shoot the target. With Adult leadership prioritizing what needs to be a priority target. So a gun team under the Platoon Commander (or Weapons Squad Leader) becomes a fairly simple to train and employ arrow in the quiver. All you need is an 11B bump to the MTOE to man however many guns you want to keep at platoon level (1-2). Doesn't even need to be MOS 11Cs (mortarman) doing the job. Because, at that very limited level of mission capability, you can train non-11Cs to handle day & night visual engagements out to max range at handheld (about 1300 meters)...
8. One day I trained members of my SF Company to crew three 60mm mortars out on a range at Ft Benning. Not a one of them was a mortarman. That was deliberate. We were planning to do a night FPF (Final Protective Fire) exercise, using all hands and all weapons against a simulated enemy insurgent battalion attack (El Salvador era scenario). So 70 or so dudes entrenched with all rifles, sniper systems machine guns, LAWs, 40 mm, Claymores, wire, flame fougasse, hand grenades, etc. dialed in on pop-up arrays starting out at ~600 meters and moving the exposure in to the final emplaced wire barriers. A completely prepared "sector" of simulated perimeter with range cards, FPF plan, wire obstacles, directional mines, and crew served guns emplaced.
Two M224 cannons were employed in handheld mode with small baseplate and no bipod or dovetailed sight. Each gun had an assigned Gunner to aim & fire, AG to hang rounds, and an Ammo Bearer to feed the AG with fresh rounds (HE & WP). Third cannon was the full gun (bipod, large baseplate, sight, and cannon). This gun was supplied with illum rounds only.
We simulated an emergency "Stand To" occurring after dark, with the entire company donning harnesses, ammo, weapons, rucks, etc. and rushing forward to join on duty LP/OPs on the simulated perimeter and man fighting positions, light bunkers, and trenches. "Enemy" pop-up target arrays began appearing almost immediately out at distance. Every man in the company passed behind the mortar firing points and dropped off 2-4 rounds of 60mm ammo. Same idea as everyone in a unit carrying spare rucksack ammo for machine guns. Something we also did by SOP back in the Rangers to feed our mortars. The idea here being to simulate hasty employment of mortars utilizing alternate positions (vice utilizing prepared firing pits with ready ammo storage bunkers). So about two hundred or so rounds available for the engagement.
As the range went hot, successive weapon systems began engaging at appropriate distances and the Hand Held 60mm gunners were smoking target arrays from the very beginning out at 600 meters. After only a day at the range learning how to 1) handle & hang the rounds, 2) handle, aim, and fire the tube using manual trigger, and 3) estimating ranges, fuzing, and charges. Medics, Engineers, Radio Operators, doing this instead of 11C or 18B mortar types.
The Illumination Gun was taught to throw up a hasty and continuous "Iron Cross" of parachute flare illumination rounds. Left, Right, Long, and Short. Keeping the entire range fan under continuous illum. Time the burnout and sling more illum into the sky, gradually moving it in, but keeping it behind the inwardly moving target arrays. They just fired rounds in a repetitious pattern, gradually bringing in the range. No guns laid in by compass or aiming circle. Just a hip shoot at (for mortars) close range.
This in a day before thermals, IR lasers, etc. The illum allowed every gun and munition in the company to find targets in the dark. A white light fight with a final expenditure of all FPF 60mm HE at minimum range against the same targets that all other weapons were engaging...at about 75-100 meters.
The guys gained an appreciation for the sheer firepower and utility of handheld mortar systems manned by essentially super-grenadiers not using laid in guns, plotting boards, or adjusted call for fire procedures. All were impressed and saw the usefulness of the guns.
My point? I can train a fucking monkey to be deadly with hand held mortars at platoon & company fight distances. So too could the rest of the Infantry if they elected to assign hand-held cannons (like that very lightweight model in the video) down at platoon level. I think the idea has merit. Ultra-lightweight mortars at that level would fill a capability & responsiveness gap. The only limitation is The Soldier's Load while on foot. How much ammo the entire force can carry on the march. Two rounds per platoon or company rifleman is not unreasonable. BTDT.
Just my $.02