I used this foot in a Bernina class (a loaner for the class) and it was very cool going around curves. BUT they referred to it as the "leather roller foot", not as a FMQ foot.
AND, why would I use it instead of my BSR foot (stitch regulator) for FMQ. The BSR is wonderful for FMQ and my stitches are all the same legnth. I can concentrate on moving my piece and it (the BSR) speeds up or slows when I do.