Sotaarms.com is a good alternative. I have one and it shoots good. C products mags are the best. The mags can be the weakPart,load them and leave them loaded to help break in springs. The bcg needs to be well lubed. And the recoil spring should be lubed well too(I used silicon based garage door lube). The breakin of shooting of the firearm will help the action too. Enhanced firing pin(slightly longer) helps with cheap russian ammo too. These helped mine to function better. Others will have their opinions to and reading theirs have helped me make mine work better. Sorry about the rambling.
Good summary of what I've read to make a 7.62x39 shoo reliably in an AR platform. Also, good to see feedback on the SOTA. I've considered one many times.