this one don't need to be unscrwed . its pricy but its also solid steel an close to a true beryl but uses a standard RSB
22515 Beryl Rail Mount - AK47 & Saiga Rail Mount  - $153.99 : Mississippi Auto Arms, Inc ::, Your Source for Saiga, AK47, AR15, Tromix, Glock, and SKS firearms and accessories
all of these use a little pin in the front. the triple hinge of the one would be likely the strongest. I almost laughed when they said its patentied . I guess
the ones that use just a screw on the tang can be had for about $30 an up some have a flip up sight included for $40 or so. some have side rails an other stuff.
any thing that touches the receiver or tang etc is going to have issues for true accuracy issues . IMO if you want to shoo these accurately you need the rail away from the receiver . I make custom cantilever set ups for my builds were I want to use scopes an expect sub moa performance.