I got my 10.5 from Frontier last week and the only complaint I have so far is the selector ring. I was also curious about the 80% compatibility so I sent an email to Mick and got this back.
Please note that all parts are interchangeable with those made by Colt and others for similar weapons. It is only when comparing part for part to those on an M16A2 rifle that the 80% compatibility occurs.