I enjoy my M&P .40 & 9mm, never had a failure of anykind with either.
I also have the M&P Shield in .40 and while it doesn't get fired as much as my full size M&PS it's never failed in any way.
The Shield is a very slim, small, light, pistol for a .40 caliber but I have no trouble controling the little beastie in rapid fire.
My reasons for the M&P 9mm is that my 12 year old wanted a 9mm since he has a 9mm R.I.A. full size 1911 in 9mm & enjoys shooting that one & 9mm ammo is coming down in price.
Wally has ZQ 9mm for just over $12 bucks/50 rnds of hardball 123 grain loaded to NATO specs (they say). That's getting closer to pre-panic prices but has a ways to go yet. I remember paying $8.99/50 for Federal 9mm about 3 years ago.
The ZQ is boxer primed, brass, reloadable.
I'll post some sort of range report on the ZQ in the RIA & M&P 9mm if y'all want.