6x7 Viewfinder Masks for Mamiya Press

So, I'm wondering. I see these viewfinder masks occasionally on EBay, and they appear to have some sort of moving part.
Is it possible that these masks include parallax correction? Once fitted on the camera, does one get the benefit of parallax correction?

 

The only moving part is a little thing that you push sideways when putting it on and taking it off. However, there is a manual parallax adjustment slider in the viewfinder. Since the parallax is mostly vertical, I would think that this would work the same for 6x7 and 6x9.

 

Thanks for the response. Just have to purchase one and give it a try.