I tried a "take-a-look" type mirror, but found that it mostly gave me a view of my shoulder and was finicky to keep adjusted. I now use a bar-end mirror, which is more satisfactory. There is some vibration on rough surfaces, but I only need to see whether there is a car behind me, not read the license plate. I tend to use the mirror in the following situations.

1. Making left turns in heavy traffic. It is difficult to continually look over my shoulder for a break in traffic.

2. When forced by bad road shoulders to ride in the middle of the traffic lane, I use the mirror to avoid having a car sneak up on me from behind. Using my ears worked most of the time, but there were a few surprises.

3. In a paceline, the mirror helps me keep an eye on the riders behind me. Just yesterday, I was pulling a group and accelerated too fast out of the turn, dropping the rider behind me. I just feels too dangerous to look back over my shoulder with someone inches from my back wheel. The mirror makes this much easier.

Out of style-conciousness, I tried riding without a mirror, but my practicality eventually won out. One other thing that I have noticed is that most older riders, even very competitive ones, use a mirror of some sort. This could be a Darwinian process of natural selection or just a triumph of common sense over testosterone.