Nice hardware! I had a 100-rnd Beta Mag for one of my AR-15s, but sold it to a friend from MD, along with a half-case of 40-rnd mags before the ban went into effect. It was a fun piece, but I found the SureFire 60-rnd mags more reliable and less cumbersome.
Those beta mags suck.
The MD Arms drum for Saiga 12 works fine.