I have the Shield in both 9mm and .45. Shot the .40 and it was too snappy for the Mrs. (she has a 9mm as well), I agree with all the info. provided on the 9mm version as previously posted....If considering the .45 version, below is my prior posting of my experience with the .45, since posting more of my colleagues have purchased and put the Shield .45 into service for back-up and off-duty carry.
So I picked up a Shield in .45 ACP with no thumb safety, added a set of Ameriglo night sights as well. As a side note, had an issue with the MGW Shield sight pusher and could only use it to start the sights out of the dove tails and then used a brass punch to remove them. Used a brass punch and homemade delrin/polymer punches to install the new night sights.
Shooting: Fired approx. 300-350 rounds at first time shooting it, Winchester white box 230 grn, FMJ and Winchester 230 grn. JHP Ranger (duty ammo) for ammo. It shot pretty good, a bit snappy compared to my 9mm Shields and G43, no hiccups or failures at all, not bragging, just didn't experience any issues. The new trigger is quite improved, not gritty at all all, smoother take up, similar to an APEX in an M&P. The new grip texture (factory stippling) was much improved, felt good and was definitely aggressive enough for my tastes that I won't need to send it to BoreSight Solutions...at least not now. Just about everyone in our dept. training unit and range staff have bought one, qualified with and are carrying the Shield .45. Overall, it was pleasant shooting and shot well for me.
The reason I bought it- currently issued and carry S&W MP .45 full size with TLR-1 lights and .45 ammo is provided, so a small compact .45 was an easily justified addition for me. It's still a bit big for BUG pocket carry (weight fully loaded is more than a 9mm Shield loaded), ankle carry is probably ok, but have not found an acceptable (to my standards/preferences) ankle rig, maybe I will contact John at 5 Shot Leather to see if he can accommodate me. So, I'm pleased with it for when I'm needing/wanting to pack a smaller gun. Still dig my 9mm Shield. Just my thoughts and experience thus far. It has not been carried much, still awaiting some Milt Sparks leather and JM Custom Kydex.