Not having a mirror was kind of dangerous for me; I couldn't turn my neck far enough to get the desired area within the view of my glasses and found myself trying to turn into an area that had only been cleared by blurred vision.
I tried contact lenses as a remedy but ditched them after a week.

So I tried a helmut mirror, and found that vibration would kill the view on rougher roads. But I liked the mirror. My solution: I braced the mirror with a second leg. It killed all vibration and the mirror works great for me now as a means of keeping track of the "big picturer" of traffic behind me.

It takes a moment to register your view of the mirror though. I've found it doesn't work for emergencies that require instant action such as a car backing into your path from a driveway. For those you've still got to crank your head around.

Mike