Depends on what you get.
If you buy their assembled rifles, then perhaps you will not get top-tier parts in all areas. For completed receivers/kits, I prefer CMMG or BCM or DelTon. But I've had good luck in buying specific parts from M1S that either they have that no others have or that are sourced as commodity items. Examples would be Shaw barrels, stripped receivers, and YHM manufacturered bits.
They clearly have a business model that has them buying AR15 bits at the cheapest cost and making kits/units out of them. Three/four years ago, before the AR boom really hit, that often meant that some of their small bits were simply not close to spec. The AR boom seems to have helped them step up a bit; I can only surmise that they are simply exposed to a better quality of part these days.
I have bought at least one completed rifle from them - a retro A1 built around a Colt 1:7" pencil barrel that they stumbled into - and it's been quite reliable.
-A conclusion is not a destination, it's simply a convenient place to stop thinking.-
-Reading a thing doesn't automatically make it so; repeating it doesn't necessarily make it any truer.-
-Every Texan should be a member of the Texas State Rifle Association.