I researched this before I got my AR-9. I couldn't find one that really was without flaws. I bought a dedicated lower. I run Glock, KCI, and a no name stick in it. Has never failed (yet).
There is an adapter for .223 Pmags. They came out after I finished mine. Seems legit keep they are getting good reports. Wish I could tell you the brand, but can't remember it.