EPArmory receivers are extremely prone to chipping (been there, done that ... as have many others); and the threads in the receiver extension boss are usually pretty rough. ...But they're rather decent dimensionally.
TN Arms Corp. standard 'hybrid' receivers have a laundry list of dimensional and finish issues. If they can't make a "complete" lower work properly and meet simple dimensions, I wouldn't trust them to get things right on an "80%" either. On the up side, you are the one determining some of the dimensions on an "80%" that are normally bad on TAC-15 (finished) lowers.
But I still wouldn't do it.
They're too busy trying to expand their product line to fix issues with existing products. People have been waiting almost 4 years to get a lower receiver that doesn't have to be shimmed to keep the BCG from smacking the front edge of the buffer tube. How long do you think it would take before they got around to fixing issues and honoring their replacement guarantee on an "80%" ...?