I'm a bit hard of hearing but love cycling. A few times on smooth roads cars had caught be unawares - not good! I saw some cyclists in the USA using the Third Eye Pro (or similar) and decided it was worth a try - I've not been disappointed. It's not cheap for what it is, but my dog considers me to be irreplaceable, so it was worth the money!
It was easy to fit to my helmet, though I added some black insulating tape to be sure it stayed put. I'd read in another review about ensuring it was fitted so I could use my dominant eye. Didn't know I had one of those but a quick search on the Internet suggested a simple test - hold your arms out in front of you and cross your hands leaving a small triangular gap between your thumbs and fingers. Look at a distant object through the gap with both eyes open. Now close one eye at a time - the dominant eye will still see the object whilst the other won't. It worked for me. The irony is this put the mirror on what logic suggested was the wrong side but I took the advice of another reviewer and he/she was right! The field of view is good enough to see approaching traffic despite it being on the kerb side of my helmet.
Of course 'serious' cyclists laugh, but they probably have good hearing. For me with my hearing disability I consider this to be as essential as my crash helmet! If they tried it, the 'serious' cyclists would see the benefits too.
In use it doesn't vibrate too much on rough roads and most of the time the image is rock steady. Cobbled streets in France were a good test and it was still perfectly useable. I found it fiddly to adjust the first time I used it whilst riding, but it's easy when stopped. If I do need to adjust it whilst cycling I wait for a smooth piece of road before doing it. After cycling it folds neatly against the helmet.
I think this little mirror is great and worth the money!
The mirror arrived in good time all the way from Germany. With my helmet - A Giro - the best attachment was on the INSIDE of the helmet on the RHS. I chose the Right side because this is my dominant eye. I think this is important. This position doesn't get in the way of my head as I thought it might. Follow the instructions carefully and the sticky pad works fine. They even provide you with a spare. They suggest that you try out the best position by using masking tape BEFORE using the glue pad. The pad can't be reused so check 2 or 3 times to make sure. The mirror gives a clear undistorted view. You can't see directly behind you because your head is in the way, but moving your head side to side to scan behind works fine. Try it on quiet roads first as it takes a little getting used to like anything new.
10 Months later 27/5/2013... I'm still happy with the mirror but the glue allows the mirror to slide around over time. I intend to use some epoxy resin to glue it better.
Initially I was not too happy with this, the first time I fitted it the glue pad started to fail and I found I could not get a really good rearward view. Upon reflection this was more related to poor prepping of the helmet and poor positioning of the mirror. Version 2 of the installation was far better, the mirror stays in place, offers sufficient rear view to offer additional safety, the mirror is robust and does not shift if bounced around and I am very happy with the product overall.
This is a clever device. I have a stiff neck and find it hard to turn around and look over my shoulder, and handle bar mounted mirrors don't work so well for me. It take a bit of getting used to (especially in relation to how you angle the mirror for best filed of view), but it works well.
This is my second one (I bought a new helmet). A little tricky to position accurately in use, needs adjustments from time to time depending on one's posture. I almost never ride without it because it is a huge advantage knowing what is going on behind. The only exception is in heavy rain when I can't see anything due to water on the mirror and glasses.
This is quite useful but it's quite tricky to get the position just right. Your shoulder tends to get in the way. With a rucksack it's even harder as your view is obscured even more. Also, it can be dangerous to keep looking behind, trying to get the angle just right. This takes your concentration away from the road ahead. I find it best to have it adjusted so that you need to turn your head slightly to the right to view behind. This swings the mirror out over your shoulder giving a better view. Nevertheless, when properly adjusted it can give an idea of what is behind especially before some manoeuvres like turning right which can be dangerous.
If you wear glasses you need to raise your head to look behind. Otherwise the mirror may be above the frame of your glasses and not in focus.
You may need to adjust it each time you put your helmet on as the mirror tends to get knocked out of position.