As far as I can tell, they are identical w/Rock River lowers, except that the finish is a bit duller, and not quite as black as RR's. If the upper you're going to use is a Bushie, DPMS, or most of the smaller suppliers products, it should give you a fairly good color match. If you're going to use a Rock River upper, you'll probably get a slightly better color match w/a RR lower.
If color isn't a major concern, go for it. It should work just fine[:D]