My FAB-10 lower wasn't the greatest. Had various issues and the finish comes off fairly easily. Wish they would just do a standard anodized finish on it instead of the painted finish it has on there. Anyways, I had difficulty with the buffer tub install (tried a few different ones too...rifle and carbine), the hole for the safety detent pin was drilled off a little OR the safety selector stops weren't milled down far enough...either way, the safety lever hit the stops....and the mounting area for the pistol grip was out of spec and too wide so I had to shave down a grip to get it to fit (I could strech fit it but then it bulged so much that it would block the safety selector ...) Wasn't installer error as I've built many lower over the past 10+ years...
Overall, I would rate it as a crap lower and if it was a "standard" AR lower, I would never buy another one but....I tried parts from Colt, Bushmaster, Vltor, LMT, etc. etc...definitely not the parts....I just bought one for shits and giggles (as I already have a few normal AR's)....I did finally get it built and it seems to work fine (dry fired it with snap caps) but I have yet to fire it....I'm sure it will work fine....
Hopefully, yours won't have so many issues...I think I would rather buy a 80% "FAB-10" lower (I think Tannery sells 'em) and build 'em that way....it's probably just as expensive to build your first one (buying the 80% and the tools) and then the rest after that would be much cheaper...