After looking at the picture on eBay it is my opinion that is a very early attachment to make decorative stitches.
It probably came with a set of cams.
I also believe it is brand specific and might not work on a machine it was not made for. Even at $9.99 it might not be useful. A low end machine with decorative stitches will do the same thing. The early Singer machines (1950's) worked ok but the system for cams was built into the machine.