I have used that light, I also have one like it with 27 LEDs. There are bike taillights the size of a D battery with only 3 aaa or two aa batteries that are brighter, and they come with bike mounts.
One is much brighter from the side too. You get a brighter light, less weight, better battery life, less batteries to buy, a bike bracket included, and more visibility from a Cateye TL-LD 1000 or a Performance flare (even brighter than the Cateye from behind).
Sorry about that, I bought one too. I compared it to the other lights myself.
you might want to see this.
http://www.bikeforums.net/showthread...=Cat+eye+light