I've never messed with the ATI.
I did buy 2 stripped NFA lowers.
The two stipped lowers ended up with CMMG parts kits, I had to use a needle file to get a couple of the pieces to fit right, they were just a little too tight on the lower. It's been a while since I messed with them, but I believe it was the mag catch and the safey holes that needed just a little bit of material removed. It wasn't enough to be of much concern.
One lower that I completed with the CMMG lpk ended up with an 18" DPMS M12 barrel and DSArms uppper.
The other ended up in the junk box for a later build.
I took the completed rifle out, fired it a few dozen times, and brought it home. It sat in the cabinet for about 2 weeks and I took it out again.
The second trip out I had brought 10 full 20rd mags to run through it and get the scope zero'd and all that jazz.
The third mag in, I fired a round and the buffer tube and stock broke away from the gun.
The rounds were factory LC rounds.
There is a mold mark on top of the ring where the buffer tube screws in on the NFA lower, my lower cracked across almost perfectly in the mold mark.
I called the dealer that I bought them from and explained to him what had happened and I wound up returning those to him for a refund and bought Stag lowers to put my parts kits in.
I called NFA and told them what happened and they seemed more than willing to oblige. The dealer was local though and willing to make things right without me having to ship the lower back to NFA.
I'm not saying the poly lowers are bad, I think I just got one that was flawed. I just got turned off at the thought of sticking a polymer lower on any of my rifles after that one broke.
For a casual shooter that just wants an ar15 to have one, they'd probably be fine, but if you're wanting a knockaround rifle, I'd invest in a metal lower.