I have the pic rail adaptor, they do have a flaw though as do the sling swivel version. The large through bolt is not fully captive and works itself loose so I modified mine to lock it, the through bolt that is, and I use a simple two locked nuts arrangement to set the cant tension, easy to convert to as was with a new tension arm from Tier One and trimming the through bolt.
I would ask £300 posted.
EDIT: I thought I had misplaced the tension arm, I found it!