rseeker

Another another vote here for Take-A-Look.

I put mine on my helmet, not on my glasses. My glasses move around a lot, and putting the mirror on the glasses would make that worse. The helmet moves on my head some, but not as much, and I get good results. I do have to adjust before every ride and make sure it's all the way pushed on the helmet. It takes some lighting (I usually ride at night) to adjust so you can see what's behind you. As long as I can see the outer edge of my ear and the top of my shoulder, it's pointing the right way.

Several people here have said, once you get used to a helmet mirror, you'll miss it when you walk without one.

I also use a handlebar mirror. That may give me a view behind even if I have to turn my head away because the sun or headlights are blasting me in the helmet mirror.