I'm a fan of consistency. My 9MM (bigger than pistol) guns are ARs. Same safeties, same way of dropping the magazines, same grips, same way to clear a malfunction, etc.
Try to do it with pistols, too. Even my striker fired pistols have thumb safeties. If I carry it, it's got thumb safeties. I no longer (for many years) carry a revolver. I stopped taking my M1A to the range (M1, too) because after using the safeties I'd find myself dropping the magazine on the AR15's next time I took to the range. That trigger finger has the need to do something after I stop pulling the trigger and with no safety in the trigger guard of the AR it finds it's way up to the mag. release and the mag. falls to the bench or ground.
I like that it uses the M&P pistol grip, magazine release, use of the pistol magazines and the storage method (I do wonder how the folks that value balance of a long arm will like loaded mags at the butt of the carbine, till you use them. Balance will change as you fire it. Being at the extreme rear it'll be more noticeable.
I don't like the safety. Different than what you carry - if you carry an M&P pistol. Under stress, you're in danger of either not using the safety (if you carry an M&P without thumb safeties) or wasting time looking for the thumb safety (if you carry M&Ps with thumb safeties.)
Just my opinion. Fun looking gun but I have my reservations.
If anyone here buys one please, please start a thread with pictures and your experiences using it. It would be helpful for all of us to hear from the people we "talk" with all the time about M&Ps vs. watching a reviewer on youtube. The more people that buy/use them and communicate about them the more things (good or bad) will be discovered.