I agree. But what a problem finding one that gives a good view of behind, not just a view of your own arm! See how i overcame that problem (photo at top)Definitely. I first got a mirror years ago when I found with a hood when it rained didn't allow looking over the shoulder successfully. I found it so invaluable I won't ride a bike without one now, a mirror if it's properly used is the best protection a bike rider can ever have.
.