Wouldn't that work with running too? It's interesting anyways. If that works, it could be even faster than turning around and WDing in some cases.
Well, with running, your character would get stuck in that slow turning around animation at the last second, and when he's doing that, it doesn't let you fall backwards off of edges.
If you're just beggining your dash and try to dash the other way as soon as you come close to the edge, you'll just move too far by dashing.
However, there is some kind of glitch with dashing backwards just as you're about to run off the edge, it takes frame perfect timing but if you dash backwards at the right time, you'll fall straight down off the edge into a perfect edgehog. So pretty much you just dash forward, then dash backward with really good timing.
So yeah, unless you can somehow master the dashing thing, i'd say walking is easier.