I think, generally speaking, those slides that are flush when extended have rollers underneath that roll up a ramp and onto the floor when pulled in. I thought in my case, that bumping up onto the edge of the flooring material would damage the flooring material so I put a strip of tapered hardwood along the edges where the slides came in, barely visible in the photo. (The previous carpet was doubled over at that location and that eliminated any small level differences that there may have been before. Darned hardwood cost more than the flooring material as it had to be milled by the supplier!!) I have seen no evidence of floor damage caused by the rollers just running across it or sitting on it so far.
I still would like to replace carpet in the slide itself but have, so far, been deterred by fastening it down on the leading edge. I believe that there is a fairly wide steel edge under there.