I use the slider for all of my FMQ. Makes for smoother quilting for circles, spirals, etc. My machine is recessed in the table and has support for back and sides. I also use the Machingers gloves and much prefer them to the other types I tried. I will take all the help I can get
And as others have said, nothing to do with feed dogs. It has an opening in it that fits around the area under your needle.