1) Is the RRA mag well block 1 or 2 piece?
2) Does it actuate the bolt hold open with Colt mags?
3) Does it actuate the BHO with modified UZI mags?
4) How is it attached to the lower?
3)no, UZI mags don't have bolt hold open on the follower
4) Goes in from the bottom, socket set screw is turned from the bottom of the adapter and two pins extend gripping the inside of your lower receiver mag well.
I bought a RR and a Colt.
They were identical.
Opinion. Stick to IMI Uzi mags - they fit much better.