Atlanta PD here.....
From my understanding the big reason we made the switch to Glock was the inability to obtain replacement parts for the M&P's in a timely manner. The M&P's were okay, I wish I had bought mine, that's a good price. If I remember correctly that's the same price we were able to buy our duty weapons for if we wanted them. As you probably know, the triggers are sloppy but easily fixed. Another issue I saw, was the slide stop / release levers would break clean off pretty frequently on high use guns. Mine was probably one of the higher round count guns and I personally broke the slide release lever off mine. The vast majority of them probably have less than 1k rounds through them, as most police don't train very often.
Be advised, all of the APD M&P's will have the magazine disconnect, so the weapon will not fire with the magazine removed.