Could NOT fit a bar end mirror on my handlebars (I recently found a way to install a bar end mirror on my curved mountain bar handlebars and thus went back to using bar-ends). The Mirror was good, but not as good as a bar end mirror. The chief problems with the Helmet Mirror related to the concept of the Helmet mirror more than a problem with the helmet mirror I had been using. The Problems I had with the helmet mirror are as follows:
1. The thing wears out, not the mirror itself, but the adjustment mechanism. To be light on a head the adjustment mechanism must be small and light weight. Furthermore they must be cheap. Thus most of them rely on fiction of plastic against plastic. AS you adjust the mirror the plastic slowly wear against each other and after a while the adjustment mechanism does NOT hold the mirror in place.
2. The mirror is small compared to a bar end mirror, this is true of Even the larger version of the Helmet Mirror (Which I used). IT is small and sometimes hard to use (Especially after the mechanism starts to wear out and drops from where it is suppose to be).
3. You need to adjust the mirror every time you start your ride, helping it wear out (Especially true if you adjust you helmet for wearing winter clothing under the helmet to keep warm).
As a whole I would go with a bar end. The adjustment is heavily built and will last for years (and easy to adjust by just tightening the bolts holding it together).
I use the Mirrycle Mountain Mirror, it is easy to adjust and if you hit something it will generally swing away from what ever you hit (Knocking it out of adjustment but it is easy to re-adjust).
For more on the Mirrcyle Mountain see their web site (They also have a bar end for Downturn Road bikes, but it is NOT on their web site). The difference appears to be that in the Mountain you have two adjustment arms rights after each other, while in the road version you are limited to adjusting it around the end of the handlebar. Looks like the road version just was NOT popular even among road bikers, if they opt for a bar end mirror they went with the Mountain Bike version given its 2-3 ways to be adjusted).
The "Adjustments" for the Mirrcyle Mountain Mirror are as follows:
1. At the bar end itself, you can rotate the base in the bar end, 360 degrees (the Arm coming out of the Bar end can be used to rotate the base if leverage is needed).
2. The arm coming out of the bar end turns 90 degree at the end another 90 degree arm exists. This second arm can be rotated 360 degree if needed.
4. At the Mirror itself which can be rotated 360 degrees.
It is a while built and designed Mirror that takes a beating and can be adjusted as needed.
http://www.mirrycle.com/mountainmirrycle.htm