The only one I owned was poly. The advantage at the time I bought was price, and considering that I wasn't going to be shooting tens of thousands of rounds I couldn't really see a disadvantage except I like the standard lowers.
I had a older one didn't think it was to bad, but then I haven't tried one of the newer ones either. So it may very well be a ton better. But for $200 on that type of point blank , get off me gun, I'd buy 1 or 2 if I had the available cash .