well apparently if you go over to M4CARBINE.net you'll find that model 1 is a dirty word but then again so is RRA, DPMS, Bushmaster, Armalite and just about anyone but colt and LMT.
I have a 9mm model1 build on a DPMS lower. it's been pretty problematic but most of it centered around magazines. they dont use great parts, IE cromed barrels and bolt carrier groups but they are an alright choice for a first time AR builder.
I would however, recommend palmetto state armory builds over a M1 if you are planning on a standard 5.56/223 rifle. they are the closest thing to milspec you can find for under 900 and you can build one for under 600 from buttstock to barrel.