Well, my CCU arrived last week, while I was out of town. Had to have a friend pick it up from my porch, we got together yesterday and I finally got to unbox it and assemble.
The unit is heavy, but not as heavy as I feared. It balances nicely. It feeds snap-caps from my CIT45CSP frame and metalform mags just fine, and that gun had a nice trigger as a pistol, so it continues to have a nice trigger as a rifle.
It was a bit less assembled than I'd imagined, they essentially put the stock and mini-quad-rail on and arranged all the other parts in the box. At first I was mildly annoyed, then I remembered that they're all standard rail mounts and happily played LEGO for a few minutes putting it together. Still need to mount the sling point and add a sling, as well as the rail for the top of the carry handle (I have a cheap red/green dot sight I intend to mount there at some point). Assembling the fire-control group to the CCU was simple and obvious.
The short M4 stock extends enough to be comfortable for me (6'3") and goes short enough for the Mrs (5'2"), so I made the right choice there. We're both used to aperture sights, so the M4 sight system I ordered (carry-handle mounted peep and turret front) should be good.
Firing and sight-in sometime this week if I can get free, as well as a side-to-side comparison with a KelTec sub2000 and M1 Carbine.