Simunition started in law-enforcement-world as a training aid, and was quickly adapted to the military for OBUA training.
It has its limitations, but it‘s pretty fantastic stuff.
We used it during Ex Stalwart Guardian, and apparently we will use it again next month at Fort Drum on a combined unit FTX (48th, QOR and RRC)... more OBUA stuff.
They mostly have adapters for pistols and SMGs as this is where it all started, but the Colt M4 upper receiver (which goes on your C7 lower receiver) is great kit, and turns your 1m long hunk of firepower into a shorter, OBUA-friendly assault rifle.
What I don‘t like are the cheap, easily breakable mags. Also, I seem to recall the mags held fewer rounds than the normal 30-rd mags ... I might be mistaken, August was a long time ago.
A few friends of mine are Toronto cops, and they all got to play with Simunition at Ontario Police College during some traffic stop scenarios, and again back at Toronto‘s C O Bick police college, they did some fun indoor stuff (judgement training, etc). I believe the tactical cops also use Simunition extensively in their training.