I'm using this with a L+M Arc light. In the w"inter" I ride at night 3 nights / wk, So-Cal Fire roads + Single track. I rely on one light at night, either helmet or bar mount.
easy on / off
side to side adjustment
Tilt adjustment is pretty easy
After waiting for this part, having been sent the wrong part 3 times, I was pretty eager to try out my new Arc with a helmet mount. Bad news bears. The Arc, while a great light, is a)decently heavy b) tall c)relies on a small base for an interface with the mount. The Light bar Mount is made out of a pretty flexible rubber. While this is great for making it fit around a lot of strangely shaped objects, it fails miserably as a means of mounting your light onto a bike helmet IF you are riding anything (singletrack, fire roads, etc..) that is, in any way, bumped, rutted, or textured. Problem is because of the weight / height of the light, the mount flexes and stretched enough that your light is now bouncing/shaking all over the place. For the first time, I have to say a bar mount is actually more effective than the helmet mount.
I previously used the NightRIder Trail Rat. While not a great light (brightness) the plastic interface / helmet mount makes for a really solid / secure connection between your helmet / head / light.