As so often is the case, after trying a mirror, I now wouldn't be without one.
The mirror lets you see at a glance if there is anything coming behind. It doesn't replace turning your head and looking behind, but it sure does help let you know what is happening behind at times when you can't turn your head.
Sure you can often hear there is a car or truck coming. But not always. Depending on the wind, you get no warning at all. Also, while you might hear the first car or truck, if there are several, you will not be able to tell if there is one or more from the sound. As the first is going past, and your concentrating on avoiding potholes, or rough edges, a quick glance in the mirror lets you know how many more.
I use a handle bar mirror, rather than a helmet mounted one, cause I didn't like the way the helmet mounted mirrors create a blind spot. But other people swear that helmet ones are best. What ever works for you - try them both. Get a mirror and discover how useful it is in leting you know what is going on behind.
