I've worn a rear-view mirror on my helmet for years. It's indispensable for riding in traffic. I can see at a glance if there are cars approaching, or if there is a (overly) cautious driver who's afraid to pass with less than a full lane clearance, or a driver (usually a young male in a pickup truck), who wants to send me a message that I don't belong on a road by passing with 2 feet of clearance. The mirror on this model is larger than ones I've had in the past, which makes it easier to use. I wouldn't want it one mm larger or smaller. I wear glasses, there's a magic position and angle for the mirror,.... just at the upper left hand corner of my glasses, and peeking over my left shoulder. I've found it very easy to get this mirror properly adjusted... and once positioned, it stays firmly in place. Very lightweight as well.
They suggest mounting the base on the inside of the helmet, and I tried it there but didn't like it, so after testing it first with masking tape, I mounted a second piece of Velcro (included with the kit) on the outside of the helmet, with the transverse bar angled outward, and the mirror hanging below. It works perfectly for me in this position. http://www.amazon.com/dp/B017H55ZR8/ #fnova