JP is reasonably well known.
http://www.jprifles.com/
Will likely pick up the upper from them as well. I guess I'm just a bit surprised that you can buy a lower that's "80%", but would take any competent machinist less than a half hour to complete. And then there's no FFL required, no need to create a serial number, etc. As long as you don't sell them, it seems like a great way (if you're a competent machinist) to build what you want without the hassle. Self reliance and all that....
Issues of fit/finish/timing notwithstanding, I kinda like this approach even though I haven't tried it yet.