Finally started my AR9 build today. I ended up going with a dedicated lower from New Frontier Armory. It seems to be very good quality in that its a billet lower with the mag release already installed. An the best part it takes Glock mags, but the one down side is that it doesn't have last round hold open. I guess its not the end of the world but it would have been nice, but from what I've read they are going to have a upper receiver that incorporates the bolt hold open feature into it. So I guess Ill grab onto one of those when they come out and swap my existing upper. Just wish Id read into them a little more first and found that out, but over all I'm very happy with it and not to mention they had $15 off to honor Dianne Feinstein, So how could I not get one when they were offering that! LOL