The Mirrcycle Mountain Bike mirror ( with mod ) is the best ROAD bike mirror available. (Picture attached)
Last summer I did a review in this forum of a number of road bike mirrors. My twenty-year old Rhode Gear mirror broke and I needed a replacement. Because of some sight issues and the need for corrective lenses, helmet/glass mirrors don't work for me ( I did try them ).
None of the mirrors I tried worked well. I liked Mirrcycle mirrors because I've used the old style mirror on my touring bike since 1986. It obviously did not fit my new bike. I also tried the new Shimano style Mirrcycle mirror. It worked OK, until it broke ( to be fair Mirrcycle sent me a replacement part free of charge, and, unlike many manufacturers, they have replacement parts). I liked it in town more than out on the road. It does have an average amount of vibration.
Then I hit on the idea of modifying the Mirrcycle mountain mirror. I took off the second, shorter arm and screwed in the mirror where the short arm would screw in to the long, main arm. Then I put the whole unit in the bar end of my handlebar. Works great!
By taking the short arm off you substantially reduce vibration and thus improve visibility. With reduced vibration, the great mirror works even better. Unlike all other mirrors, Mirrcycle uses a high quality glass mirror, not a plastic one. They also don't reshape the mirror much. It isn't as convex as many mirrors. This does result in a very small blind spot off your left shoulder.
Now, I can see back a quarter of a mile. This is great when traveling out on country road where the cars are going 60mph. Also, this is the first mirror that I will rely on solely to see if there are cars before making a left turn. With others, because of the convex shape or lack of clarity in the mirror, seeing and being sure were always an iffy proposition.
Another advantage is the ability to adjust the mirror quickly on hills or if you're posting. A slight adjustment will allow you to see behind you on descents. And this set up allows you to see. I've gone 50 mph on descents and still had a clear rear view.
One disadvantage is that your arm may partially block the view in some positions. This bugged me a bit at first but after a short while I would unconsciously move me arm to slightly to improve the view. Also, you can bump the mirror when going into the drops. Finally, you need to look down and out to see the mirror, as opposed to a quick out glance with the Mirrcycle hood mounted mirror. This does take a fraction more time. That is why I like the hood mounted mirror in town. But, out on the road, where I do the majority of my biking, this hasn't proven to be an issue.
If you want to be a real mirror geek, you can mount both, one on the hood and one on the handlebar end. I did do this for a month or see this spring ( until the hood mounted mirror broke, see above ). I liked it but didn't feel the need to replace the hood mounted mirror.
Mirrors are right up there with hi-viz clothing and helmets in the safety pantheon. Still, I see few riders, other than some weekend recreational/trail riders, with them.