Strengths: Good view behind, good if you ride in traffic
Excellent when standing on the pedals, since you then can't see through a handlebar mirror, vibration is reduced when standing
Weaknesses: Awkward to adjust (easier with practice)
Vibrates badly, especially when seated on the saddle, and especially when going fast. It's better on a smoother road surface. The vibration can be bad enough that you can't really see what is behind you
The mirror droops due to vibration. I have to readjust it approximately every 3 - 4 minutes; this makes it close to useless. Pity 'cos it's really good when correctly adjusted, and when the road surface is smooth.
Great idea, I love it - it just doesn't work very well. I may give up with it, and I may try a different make