http://www.daystyledesigns.com/freemotionfoot.htm
Here's Leah's modification - the part where she clips it starts at abotu 4:50 into the video.
I don't know the advantage of the metal feet - although that's what I use. Mine is actually shaped like a curcle with the opening to the front. I have used the generic hopping feet too, although that was before I learned the nice modifications.