This is what they told my friend when they gave him his money back. I confirmed it with my TEXAS DPS Trooper Neighbor on that 45 CCU and he was right.

The illegal side of these uppers is that they permanently convert the legal status of your pistol frame into a rifle frame. If you attach the Mech Tech to your 1911 pistol frame, then you cannot legally revert that frame back to pistol form unless you first REGISTER it as a Short Barrel Rifle via ATF Form 1.* This is not new. This has been a problem for about 3 years now.