Supreme Slider is good. More work than I imagined to keep it clean ... it's time to go buy more Baby Wipes already. ugh!
If you're going to get that, you should also own a pair of Machinger's (or at least some kind of grip-y gloves). If not, I would get the gloves first. I love my Machinger's. They make a huge difference in the consistency of my FMQ stitches. The Supreme Slider is nice ... especially for reducing muscle fatigue, but I can still FMQ okay without it.
Also, make sure you tape it down so you don't ruin it because it can slip & slide and I know some people in my quilting guild said they chewed theirs up within days of getting it (and then never bought another one because they are kinda pricey).