Although I agree the Supreme Sliders are overpriced, I do find using one makes a big difference...not the the quilting so much as the quilter! I have FM quilted on: my machine table (Juki, Bernina), Sew Steady tables, vinyl, and Supreme Sliders. I votes for the Supreme Sliders every time...they offer much, much less resistance than any of the other surfaces do, and that means I do not have to engage my shoulders and arms as much. I can move my FM with the lightest of touches.
I will be happy when sewing machine manufacturers put out machine decks that are themselves Teflon coated! Then I can trim my Slider to expose my bobbin access hatch and not have to move the slider off the machine bed every time I have to change the bobbin (I have a Juki 2010Q and there is no side door for the bobbin, allowing you to change the bobbin from under the sewing table...you have to go in through the top, garg). Until that day I will likely cut up my Supreme Slider (eek!) such that I can open the bobbin hatch without removing the slider.