Almost every M&P user is happy, only few are unlucky.
I must be unlucky. I was issued the original "full size" M & P 45. I ended up going through multiple pistols personally. At one point S & W, or the distributor, replaced my entire agency's "fleet" of the handgun. Everyone went through at least 2.
The agency finally got smart and ditched the thing. Our problems ran from front sights falling off, rusted magazines, premature magazine spring failures, cracked followers, rusted slides, rusted internal parts, broken extractors, broken strikers, and many other broken internal parts. Quality was horrible.
Let me say, prior to the M & P, we issued the 4566. Heavy, but I trusted it. I did not trust the M & P. It is a tad unnerving working and constantly wondering if the darn thing would work when you need it.
We replaced it with the Glock 17, Gen 4. What a superlative pistol. Almost every agency in our area? Yep, that's right, replacing their M & P pistols.
I will give the gun credit: for a 45 it was quite soft shooting. The trigger was a nightmare, but when it worked it wasn't that bad to shoot.
As I travel and attend training across this state, I am seeing fewer and fewer M & P pistols in LE holsters.
While I think the M & P line has enjoyed limited commercial success, I really don't think it has enjoyed the wide spread LE success that S & W anticipated it would.