I get a kick out of people thinking this is for the featherweight - I think Singer came out with the walking foot before the featherweight. Not that it does not fit on a featherweight, but it also fits on a lot of other Singer machines.
But it seams as long as someone says "fits Featherweight" they get more $$ for it.
I have one, and was very happy to get it for $500 several years ago. Prices go up and down for any collectable item.
As to the Decorator - you can get them for several different machines. However that one is set up for a White, so wouldn't fit on any Singer machine. It sort of looks like a side clamp, but it clamps to the bar after the top clamp adaptor is removed. Kind of a drag to take on and off being that way.