For mirror users, this should be an interesting post. I've been doing a test of three great cycling mirrors the last few days (from L-R:
Take A Look Mirror,
CycleAware Reflex Mirror ,
Efficient Velo Tools' Safe Zone mirror).
The Take A Look and Cycle Aware mirrors are fairly common and can be purchased at many LBS's and even REI. The EVT/BicycleToolMaker Safe Zone mirror isn't so common, but it is really an interesting and great mirror.
Take A Look MirrorThe TAL mirror is the first mirror I ever owned. It's simple to use and very robust. The mirror clips on to the arms of your sunglasses and stays on with a pretty strong friction fit. From there the mirror swivels and you can also bend the arms (usually not necessary) to get it in the right spot. It is relatively light weight and after a few hours of use, you hardly notice it.
The TAL is a great mirror and really, my only gripe is that you have to be wearing sunglasses/glasses to use it. If you have dark shades and you commute at night, it either means forgoing a mirror completely or getting shades with replaceable lenses. I have lost two of these because I have a terrible habit of misplacing my sunglasses.
CycleAware Reflex MirrorThe CA mirror solved my mirrorless situation due to misplacing my sunglasses. For me, I prefer helmet mounted mirrors since I always ride with a helmet. I don't have to fiddle with changing lenses on glasses (that I have a feeling I will ultimately lose :).
With the CA mirror you have to semi-permanently adhere a ball-joint attachment to the side of your helmet. The arm (the socket end of the joint) snaps on to the adhered portion. From there, the mirror can be rotated on the joint or you can articulate the arm of the mirror or you can also articulate the little ball joint on the mirror itself.
Of the three, the CA mirror is the most easiest to finely tune. There are lots of points of adjustment, but at the same time that means lots of points of potential failure. For one, the included adhesive doesn't last very long. I usually sand down the helmet and use Super Glue and a C-clamp to make sure it doesn't pop off.
Also, over time, the various plastic ball joints wear and don't quite hold their positions like they use to. To solve this, CA, sells a replaceable parts kit for their mirror.
Another issue that some may have with the CA mirror is that it is vertically oriented and not horizontally oriented (like the TAL mirror). Going from a TAL to the CA takes some adjustment because of this, but you'll cope.
With all these issues, it is still a fine mirror and I have used one with great success for almost two years.
EVT Safe Zone MirrorThat leads us to the EVT Safe Zone Mirror. The EVT mirror is easily the largest mirror of the three. This is the HD of bicycle mirrors! You don't have to worry about orientation because it's round and it's HUGE. Now for some, me included, this can be a bit strange at first. Surely, something that big in front of your face has to cause a big blind spot. I've found in the few weeks I've been testing the mirror that your eyes adjust and you can see "through" the mirror, so to speak.
If you can get over the size and Alien-esque lock-line articulating arm, the view is fantastic!
Mounting can be a little finicky, depending on your helmet. Unlike the CA mirror that uses adhesives, the way you mount the EVT mirror is by using zip ties. There is a large spine with slots and you run ties through the slots and through the vents of your helmet. It took me about two different set-ups to find one that I liked best.
The CA allows you to place it exactly where you need it. The EVT gives you a stronger mount, but you may or may not be able to get it exactly where you want it depending on your helmet's vent pattern (won't work on Nutcase helmets).
You adjust the mirror by 1)using the palm of your hand to move the mirror 2) using your free hand to hold your helmet still. This is necessary because the articulating arm has a pretty tight friction fit. With the CA, I can usually just position it with two fingers. The EVT is a two handed affair, but this is good in the long run because the darn thing won't ever be shaken out of place. This has to be one of the most robust bicycling mirrors on the market.
Now, this great view and sturdy build come at a price. The EVT retails for around $40, about double the price of the other mirrors and it isn't widely available yet (the inventor encourages you to encourage your LBS to carry it). However, it should be the last helmet mirror you would ever need to buy for a long time. I'll write another longer term follow-up after a few more months of use to see if the friction fit is still as tight.