I had an issue with mine but it was minor. I bought a German K parts kit and sent it to Tom to build into a SBR using one of his receivers when they went on sale. Also sent a magpul mag for 922r reasons. Its still pending a form 4 but I did get a chance to shoot it at a local shoot where the dealer brought it out for me.
The US made mag release he provided would not work with magpul mags including the one I sent that was returned with the gun without a fight. They should have caught this. My dealer and I swapped some parts around as he has a tommy built sl8 conversion before I ran home and grabbed the german mag release that came with my parts kit. That fixed the issue and the gun now will work with both the magpul mags and the german ones. Now to be clear I didn't give Tom a chance to fix this, I had the German part and it took care of it. If I didn't though I'm not sure if they would have sent me a different one to try or have me mail the gun back.
The plus side? Gun looked good and when we took it out it was close enough on accuracy wise to ring steel at 100 yards with the kac sights on it. Didn't have any other issues although I don't have much time with the gun yet.
Most of the issues I've heard of with the guns are where people bought the receivers and assembled the guns themselves. Some fitment issues came up or some needed a longer cam pin. Haven't heard much from people that had him build the guns so I guess I was a little unlucky but at least I had a spare part that fixed mine.