Do you know what a Plum Crazy lower is?
It is polymer,
Polymer lowers aren't for everybody so as far as resale I stick with aluminum. The parts on the polymer lowers are different as well, and I'm not sure about interchangeabilty. Armalites AR-180b rifle was a polymer and they had issues with the front ears breaking or getting worn out.
People always compare it to Glocks receivers but the two are engineered completely differently and have different stress points, not to mention, you're comparing a rifle and pistol round.
PSA lower $50
PSA LPK $45
PSA stock kit w/buffer and spring $50
Total: $145 That's only $20 more than the Plumcrazy!