It works very well, certainly the best coin-cell flashlight I've ever seen. The clip works well on a cap brim, keeping in mind that you won't get as much output and runtime as you would with other form-factors. The tube around the LED is removable, once. I managed to do it without destroying the light. You might not want to, though, as the glare is noticeable when it's clipped to the cap brim after that.

I don't use headlamps a lot but when I do I prefer one that's AA or (more commonly) CR123A powered and with a lot of output.