Dan--I haven't had one of the TBAC 223 cans in hand but if they're built like the big 30P1, the quality and precision will be superb. But really who cares about that in a can for a fighting AR? I just want a durable can that has a repeatable POI shift.
I have a SF Mini that I paid $1050 for, not counting the QD mounts, and would choose it over a TBAC 223.
Those Gemtech cans look good and seem to get good reviews. Have you asked on M4carbine forum?