FW=Featherweight. The foot shown is one of the older ones originally made for the machines. I use a modern plastic one that my machine likes. Whichever works.
You seem to know more about this FMQ on the FW than I do. Maybe I shouldn't use this older foot that came with this machine when I bought it. Would I be better off getting a modern plastic one?
Here is a little video showing someone free motion quilting with a FW:
I just got one today, can't wait to play!