If you can get an aluminum lower, that sounds like a really nice stick for the price.
STAY AWAY from the polymer receivers! I have personally seen (2) Carbon-15 (Bushmaster Brand) lowers that have cracked from "normal" usage.
I would be really curious to handle one of these and check for the usual suspects (tight fit, loose connections on Gas Key or Gas Block, mate up between upper and lower, etc).
If it passed the inspection test and the aluminum lower was included, for $805 that is a rifle that sounds like a winner.