I have never used a mirror on my bike before, but noticed this one on a bike here at BF50+ some months ago and thought I would give it a try. I finally got around to doing the installation last week and after a few test rides I can now give a report.
Assembly: Assembly and installation is pretty easy if you read and follow the directions. A plastic shim or 1/2 shim, both included in the packet, is required for some models of STI shifter. The screws and nuts used in the assembly go together very tightly... so much so that you might think something is wrong. But this is explained in the instructions and is part of the design.
Effectiveness: The positioning is above and outboard of the STI hood and the mirror gives a nice view to the rear without shifting your eyes off the road ahead. Vibration is not a problem and the image behind is quite steady. The mirror stays in place very well but occasionally a serious bump in the road will jar it out of place a little. This isn't a constant problem and is just a very minor inconvenience. Tightening the screws might reduce this but it seems so minor I haven't bothered with it. A nice feature is that you can fold the mirror back out of the way when parking the bike or loading it on a rack.
Conclusion: This thing works a lot better than I expected and I will be putting another on my #2 bike. I have never seen one of these for sale at a LBS around here, though they do have the Mirrycle Mountain version in one shop.
I'm giving this a four smile rating:
If you are thinking about a mirror, this one works well for me. I have not tried others.
Thanks to TSL for the recommendation.