IMO, 'single leg horse' stance is an excellent way to develop balance and strength, both important qualities for kicking.
The problem I see is that using it as a fighting stance is a fallacy. It greatly reduces mobility and produces a very akward (both to use and to learn) footwork.
I would opt for a more useful fighting stance, but it is an invaluable training tool.
Sapere aude, Justin.
The map is not the Terrain.
"Wheather you believe you can, or you believe you can't...You're right." - Henry Ford