A glasses mounted mirror lets your vision sweep across the whole view behind, with just a slight turn of your head. It's unnoticeable when looking ahead, after a ride or two. A few years ago, I was walking down the hall at work, heard an odd noise behind me, and without thinking, turned my head to use the phantom "mirror" to see behind me.

I've never used a bar end mirror, but it's field of view must be pretty small, and some are convex, so "objects are closer than they appear"

Even with a mirror, I'm still regularly surprised by cars passing. Unless they have loud tires, I don't hear them due to wind noise, and I have to move my head a little to see behind, so I don't do it continuously.

I don't think mirrors are a solution for texting drivers. Last weekend, I watched 3 or 4 (non-texting) drivers stay in the lane, on a course to miss me by just a foot or two, and wait until the last seconds to move over the center line. They all actually passed with 4 or 5 feet of clearance, but it's really annoying.

My main mirror uses:

--Keep track of other group riders. Are they falling behind, or right on my wheel?

--Left turns in the city. It's great, I can keep track of a break in traffic to smoothly slide over to the left lane.

--Taking the lane in the city, well away from parked cars. If nobody is stuck behind me, I'll ride in the left tire track.

--"Managing" passing cars. On country roads, there's normally not too much traffic. So I've gotten in the habit of looking in the mirror if a car is ahead, coming in my direction. I don't want to be surprised by cars trying to pass with oncoming traffic. I'll move out into the lane to "block" a car behind if I think they will be trying to pass right when an oncoming car is in the other lane--and then I can see if the car behind is actually slowing down.

I'll do the same thing, take the lane, when sharp blind turns are right ahead. Drivers can be really dumb when passing.

--Riding out in the middle of the lane when I have the road to myself. I can get away from the right side of the road, away from torn up pavement, when there's no cars visible behind. That can be much smoother riding.

--avoiding potholes and torn up roads. Can I safely move over to the center of the road?

--Tracking cars way back. If I happen to see a car way back in the distance, I can easily keep track of it. Some of them need a helping wave to get them to pass even with good sight lines.