I crowd-sourced an 80% lower thru Rockethub, and the durn thing is finally shipping. The reason I bought it is to write about building your own lower for the blog, but the time and money needed to complete the thing makes it a dodgy proposition compared to all the cheap complete lowers out there.
And I have a polymer lower, one of the last of the original CavArms builds, and it works great, no issues with it at all.