The sew steady has markings, in looking, it appears the supreme slider does not. I keep mine on my machine for piecing and lot the markings. I also love that it overs all the transitions between my machine and table (it's an industrial) so nothing ever gets caught and flipped on me. My bobbin loads from the underside so I only remove it for major cleaning.
I don't FMQ on the machine I have the sew steady on, so no idea how it works for that.