Heres a shot of my restricted (only) open bolt sterling smg. This is the second one I have owned, the first one now resides in Calgary as a TSE range gun. The open bolt thing is a US BATF rule; it is not one here. The term up here is "not easily made to fire F/A.'
Like all sterlings, this one functions fine with sten SMG mags. Of the many various sten mags (and trust me, I've had quite a few) I have had very few mags which ever gave me a problem with this gun. The story of the sten mags being crap has been stretched somewhat. They have a double thick lip, so they'll open beer bottles, and keep on shooting, long after many of the single lip variety have given up.
I take this gun to the range about once a month. Reliable, accurate, and surprisingly, almost no recoil. The only fault I have with this sterling is that it is so much fun to shoot, you lose count of how many rounds you have fired, and it seems like those lousy 5 round mags are always empty.