Being a long time bicycle commuter and tourist, I've tried almost every type of bicycle mirror there is, and I've never been impressed. Helmet mount, handlebar mount and glasses mounted, they all left a lot to be desired. The latest purchase was the last straw. In two months, the plastic ball & socket adjustment was so loose that it wouldn't hold an adjustment and, like all the others, vibrated so much that the visibility was terrible anyway. I got ticked off decided to make one myself. I made my brother one also, and he says it's an order of magnitude better than any mirror he's ever used. After years of using it, I have to agree.
Some words in support of helmet mounted mirrors- when the mirror is mounted on the bike, it takes a big mirror to get the image size you need to see anything, and thus is heavier, and the only spot you can see is directly behind you, because it can't move. Helmet mounted mirrors have the same image size with a much smaller mirror due to the proximity to the eye, and less weight. Due to the close proximity to the eye, you can just turn your eyes to get the required view whereas with a bar mounted mirror, you have to turn your whole head. This takes longer and takes your eyes further from your line of travel, and so is less safe. I find my typical glance behind is two seconds. But the big point with me is the fact that you can scan behind you with a helmet mirror by turning your head a little. A prime example of this is a long curve in the road. You can look back around the curve for upcoming traffic, something a bike mounted mirror simply can't do.
The unsupported length of the Steady Eye B's arm is only 1-1/4" and made from 0.092" stainless steel rod, so it doesn't vibrate any more than your head does. This arm is brazed to the stainless steel clips. The ball on the end of the arm is likewise brazed. The joint friction is adjustable should it need it, unlike the plastic mirrors' ball & socket joints. There are no adhesives to mount this mirror. It just clips onto the helmet visor, baseball cap or visor, and can be moved from one helmet or hat to another very easily. Maximum grip for the clips is about 1/4". If the mirror ever craps out, as mirrors in the great outdoors are wont to do, it can be replaced for around $6, $5 when they are on sale, at Harbor Freight Tools, item # 7361. This is WAY less expensive than replacing with any other bike mirror, which makes the Steady Eye renewable on the cheap! You can't do that with any plastic mirror :)
In the event you should go for a ride in New Zealand (something I heartily recommend), I can also build you a right hand version for the other side of the road.
It turns out that these are great for rowing, too. Just clip it onto a baseball cap.
TAKE NOTE - THIS IS A VISOR MOUNTED MIRROR AND WILL NOT WORK ON THE HELMET ITSELF.