It's been suggested before, but buy plates first then choose a carrier.
As for determining your probable threats - what calibers is your department seizing in the field or not?
If a specific caliber &/or load isn't listed, identified then it probably was not officially tested. Now that doesn't mean no one has shot that round at that plate just that it wasn't done officially.
Have you reached out to a competent Hesco dealer, run your situation & needs past them, and gotten their recommendation? More than once over the years, I've gotten on the phone with reps from US Armor, Point Blank, Armored Mobility, and AT Armor.
I have reached out to a dealer and they have been very helpful. They recommend the 3810 if 7.62x51 is a threat in my area, but I've never really come across it nor have others I work with. I'm very new to purchasing rifle plates so I don't want my ignorance steering me in the wrong direction. I like the idea of having 7.62x51 protection; however, maybe it's not a significant threat and I should be looking at the U210 for the weight savings and how thin it is.
I'm hoping someone with some experience that has been involved in large department purchases either on the decision making end, or receiving end, help push me in one direction. I figure it's either go with the U210 which is a fantastic plate with solid threat protection, lighter and thinner. Or go with the 3810 because it has the additional threat protection, but thicker and heavier.