P.S. - I have eight or more different types of darning feet/free motion feet, from the antique to vintage to modern. From that little $3 thing to a $40 Juki hopping foot.
All of them are meant to do the same thing whether you're doing darning, free-motion embroidery or free-motion quilting. They momentarily press down on the fabric to hold it in place while the hook catches the loop of thread formed by the needle. The mechanism is different and the name is different, but the use and purpose are the same. :)