After a couple years of having no footrest for my home desk, then trying a now-defunct subwoofer, and about two months of relative satisfaction with a small Amazon box, I finally decided to indulge my ergo urge and sprang for a Webble, an effortlessly-gliding, four-castered footrest that resembles a mesh-covered Pringle. It's taken me this long to write up a review because I've been too busy not being uncomfortable while working on other projects.
The short version? It took some getting used to, but now I'm sad that I don't have one at work.
Since the Webble is a bit thicker than the cardboard box it replaces, I had to raise my chair a bit in order to make my knees feel right. This has emphasized certain other ergonomic problems in my current chair (a POS from the Office Max up the road that's got to be close to 10 years old at this point), which means now my upper body wants to be spoiled too. It also doesn't feel cquite right when I'm wearing shoes, but I think that's because my proximity to the wall means that I can't quite put my feet where I'd like to with shoes on.
In sock feet or bare feet, though, it's just about perfect. I alternate between using the front edge, the top sides, the top ridge, and the open mesh area in fairly equal measure, shifting naturally whenever one of my legs wants to move. I also find myself partly rotating it quite a lot, and quite often I'll absentmindedly spin it around or pop it up like a skateboard. I find myself really missing it at work, where I use a static footrest that helps but isn't nearly as much fun as the Webble. Plus it looks a lot classier than a cardboard box.
If you spend a lot of time in front of a computer, little comforts can go a long way toward improving how your body feels; you could certainly do worse than this delightful companion.