After having our carpet replaced as a result of some "belly tape" peeling back under our kitchen slide and ruining the carpet, I was looking for something to help protect the carpet and looked at the ones you mention.
After thinking about it for a while, I made a trip to Office Max and bought one of the plastic floor mats that office chairs roll around on on carpet with the little "teeth" on the bottom. I cut a piece the size I needed and use it under the kitchen slide where the offending tape was located. I think I paid about 10 or 15 bucks for the mat and there's plenty left to make a couple of more if I need them.
I've encounted the same problem as some others, I have to bring the slide in an inch or two, then put the mat under the edge of the slide and stand on it until enought weight is on it to hold it in place.
With the little teeth on the back, I would not use it where it would rest on anything but carpet.