I was issued an M&P45 in 2009. We had a new sheriff and he wanted to issue handguns to deputies and wanted everyone to carry the same handgun, so he picked the M&P45. We were issued them, literally, the same morning we qualified with them, with new Level 3 holsters.
Qualification scores immediately dropped 10%. Most of that drop in scores was us not being familiar with a new handgun and holster. In my case, I literally walked to my truck, took my 1911 off the gun belt, strapped on the M&P and walked out to qualify. I managed to qualify by the skin of my teeth, but I had never shot any plastic-fantastic handgun. Not a Glock, certainly not an M&P. It was a learning experience.
I've carried it now for four years, and I'm becoming more comfortable with it. Our department scores have climbed back to the level where they were and they were before the swap. The M&P seems to be a fine firearm. I've got about two thousand rounds through mine, which isn't much, but I've learned that it shoots lead bullets as well as jacketed, and that it will digest my favorite handload, which is a soft load I used for paper-punching with my 1911s.
Learning the reset is problematic, but it is there if you know what to look for. I can feel the trigger reset without too much concentration. The adjustable grip with the included inserts is a nice touch. The M&P45 is certainly a workable gun. It seems fairly rugged, the sights are nice, and if you like plastic firearms it might be just the ticket.