Great choice too! The only 'defect' is the plastic lower. Original Ar18/180s had a heavy sheet steel lower which, I think, was more substantial. At any rate youll have loads of fun w/ it.
I don't see it as a "defect". Polymer gun parts are more than proven at this point. Glock, Sig, HK, etc.
Armalite is also thinking about making a version with a Picatinny rail, and a .308 version.