It looks really cool and I'm sure it works, but given that a USC is about 35 inches in length (about the same length as a 556 carbine with the stock out one notch where most people can square up to their target), the USC weighs 6 pounds (about the same as a lightweight 556 carbine), and the ones I've seen cost between $1500 and $1700 at the LGS (whereas a Colt AR 6720 costs about $1000).
What do the larger, heavier .45 caliber carbines buy you apart from ammo compatibility with your pistol? If it's a house gun, then that makes more sense.
If it's a SHTF gun, why would you ever use a .45 caliber carbine when plenty of Colt AR's and Arsenal AK's can be had for less money?
I like .45 caliber handguns and have shot them for years, but if someone gave me the choice between a lightweight semi-automatic Colt carbine and a real Thompson submachine gun, I'd take the Colt carbine every day of the week.