I haven't read the reviews for the M&P AR. So this may or may not apply. However I have some experience with weapons as a weapons mechanic in the AF and an armorer avocation since.
You realize the only GUN part of the AR platform (and most other firearms) is the lower receiver. It's the serialized (if it's not a self-completed 80% lower) LEGAL firearm that is controlled via NICS checks. The other parts are all accessories.
I have worked on many AR's. I am not going into detail here on what I've done or what I have. I'll say this - you can't go wrong with this AR if you can find one especially NIB. S&W backing it up is a plus. You can mix & match parts if you want to change something, particularly if it's "mil-spec". The design is universal. If you want a different trigger you can drop in performance trigger units with no machining or gunsmithing ability eg. Timney's models. Or you can take apart the fire control group and change or replace anything there including match triggers that aren't drop-in assemblies like Geissle. Here's Colion Noir's take on drop-in triggers:
https://www.pewpewtactical.com/best-ar-15-triggers/You can change the upper receiver, vary the caliber you choose (limited somewhat on what mags the lower receiver will support), change barrels and bolt carrier group, change to piston driven rather than direct-impingement, go for chrome lined, or bull barrels for competition, with or w/o forward assist or dust cover. You can change the sights, have optics, lasers, lights; so many choices. The platform is very configurable and parts are mostly interchangable. MidwayUSA is a good place for parts at good prices. So is Cheaperthandirt but some don't like them for policy reasons.
Go for it. And soon. Before Pres Harris FUBARS it up.