I hope that everyone realizes that this design is not working and is pretty much worthless.
the grinding angle need to be set between the stone and the lower edge of the knife, but this design is setting the angle between the stone and the upper side of the knife.
if you have a thick and a thin knife (without having a flat site in the area of that tool) you will end up having different angles.
a design like that can only work if the reference point for the angle is parallel on both knife sites. (edited)