I have not read too many range reports yet. I don't remember if it was here or M4C.net, but the rifles appear to have been built with what ever parts were available (may or may not have an auto bolt, various barrels, other components). They should all be chambered in 5.56, so you can shoot just about anything in the .223/5.56 flavors. Me - I'd run Federal/Lake city M855 or M193 only, then maybe a few boxes of SD ammo.
I do recommend doing a good looking over of everything before you buy. Front sight stability, castle nut, upper receiver end plate, gas key staking...If you have some P-mags at home, I'd bring them (empty and clean). I have read a lot of hit and miss with them accepting/functioning with the P-mags.
The price you listed is a better deal for what I saw them going for a month or two ago for what I observed in the quality.