Stercomm,
I use the one which attaches to the glasses. They are not very expensive (under $10). Require little adjustment during a ride. And are easily used on multible bikes. A slight twist of the neck and I can see what's behind me while still looking forward. I started with one about 4 years ago and don't like to ride without it--- even on trails. Good luck!
__________________
Bob
Enjoying the GA coast all year long!
Thanks for visiting my website:
www.freewheelspa.com