Thanks Knotted! Very helpful. Do the Guppies bounce around on your helmet?

I have a smallish Cateye light that actually attaches to my helmet quite easily and securely, and in such a way that it doesn't affect the fit at all, but I actually really like using that light on my handlebars instead (I like having two lights on my bars at night, one steady beam and one flasher). Plus I like the idea of having both a white front light and a red rear light on my helmet.