I have 2 Janome machines with extension tables (6260 and 7700) I do have a bit of catching on the corners when I have a particularly heavy or large quilt on the go. I stopped using the supreme slider after I stitched it to the bottom of my quilt 4 or 5 times. It was just too small to be effective. They do have a larger one now, but the price is larger too. I found a silicone mat for a microwave. Found them at my local surplus store for $6, so I don't know where you'd get them, but they're made by Wilton. It's 16" x 16" and sticks down quite well. I cut out the area of my needle plate - because I have a top loading bobbin - that way I don't have to take it off to change it. The edges are taped down with painters tape.
It is a good solution for me. Keep in mind that I use a very large dining room table for sewing, so I have about 4' x 3' to the left of my machine. For really large quilts, I put the extension leaves into the dining room table adding another 18" of space.