Originally Posted by
Giant Doofus
I like your rules! I've been looking at a Mirrycle MTB bar end rearview mirror. Does that seem like a good choice?
I wear prescription eyeglasses so Take-a-Look eyeglass mounted mirrors are my choice. In fact I wear both left and right eyeglass mirrors and have posted about the
advantages. They require the least head motion, just a lateral glance to look behind, instead of a head turn away from the forward line of sight as with no mirror at all.
Any mirror though, is better than none at all requiring a head turn and complete loss of forward vision;
not as described below:
Originally Posted by
Leisesturm
…It can be fatal to smack into something ahead of you because you are busy monitoring your mirror…You must learn to believe in the relative competence of other road users and focus your attention on what is ahead. Your ears (if they work) will tell you all you really need to know about what is going on behind you…
”Trust me…I’m a cager.” 
Originally Posted by
Leisesturm
…A mirror is a tool for planning offensive maneuvers. I really get tired of hearing how wonderful a tool it is for defensive protection…
If you like my “rules,” I hope you’ll follow Jim’s Law of the Road:
“No matter how well-paved or lightly-traveled the Road, a vehicle is likely to pass on the left as you encounter an obstacle on the right.”
Besides just
offensively monitoring the upcoming traffic, a mirror can save split seconds when you have to
defensively avoid unexpected obstacles and evade approaching traffic, while still maintaining near-continuous forward vision.