I believe it is meant more as an adapter for firearms that already have a picatinny rail at 6 o'clock on the stock forend. It does away with the normal mount so it sits lower. Nothing more, nothing less.
RRS makes a similar adapter but it uses a twist knob (instead of 2 hex screws) and works for both arca and pic rail. I've got a couple Harris with them and they work and hold up well.