I have an M&P40 with 5,300rds through it.
Short answer, I would never buy another one and if I could turn back time, I would've bought a Glock.
Don't get me wrong, I'm keeping mine until I shoot it apart, but based on my experiences and others reporting the same, I would never buy another one or recommend it to another person.
The extractor is seriously poorly engineered, at least for the 40sw and 45acp models. It is universal and is used for 9mm, 40sw, and 45acp but the last two calibers seem to have the most problems. It seems as if the extractor doesn't sit right. The claw cannot grab enough rim area on the case head. The slightest bit the chamber is dirty/caked with carbon, you will have problems.
Steel cased ammo is reliable through my M&P. I've shot boxes on top of boxes without a problem, but steel casings do not obturate in the chamber very well and let carbon build up on the chamber walls. I've found that if I don't clean the chamber, even after one box of Tulammo, then shooting brass or aluminum cased ammo is going to be a nightmare. Nothing but fail to extracts. Starting with a clean chamber, however, I'm able to shoot a few thousand rounds of brass or aluminum cased ammo without cleaning and with zero issues. Fun times......
P.S., the chamber needs to be properly chamfered, particularly under the barrel hood. I know most pistols aren't built this way but the sharp edge under the barrel hood is a big problem with cartridges that have sharp case-mouths, like Fiocchi for example. Some people may blame the ammo, I don't. The barrel hood and top side of the chamber should be one straight and flat surface and not have an edge. That's the cause of half of fail to feeds.
The M&P is far from "elite". I believe the pistol started off being designed by a competent engineers, then the project was given to a couple of morons who bought their degrees in mechanical engineering from craigs list.