Mine is the most accurate pistol I have owned, and that includes a P229, P239, Glock 23, and an FNX Tactical with RMR. I've got a Salient Arms flat faced trigger (which I LOVE) and frame work, along with 10-8 sights (red fiber front, black U-notch rear), but the barrel, mainspring, and slide are all stock and I have supreme confidence in it. Even more so than with my Salient Tier 2 M&P9c with a match fit barrel. Just make sure you get one with a 3rd revision barrel. It will have 2 dimples in the underside.
FWIW, I hate the plastic hinged 2-piece stock trigger on all of the M&Ps. Not just because they are gritty and heavy, but I feel like the 2 piece design just lends itself to a rather vague feel that keeps these pistols from being as shooter friendly as they could be. I like a clean, crisp wall with a predictable break and a short reset.