Magicshine is a great light, but the o-ring mounting band is not the best. So, instead of the o-rings, I used several ouchless hair bands to mount the light. I used about 5 or 6 of the very small ones (about the size of a penny).
The downside is the light is hard to remove, but that's ok for me since I ride my bike from 5:45-7am on a bike trail near my home and leave the bike in the garage aftewards. I don't have to worry about locking the bike up and using the bands gives me the advantage of not having the light slip when i touch the button.
Here's the bands (I used the black ones, but that's the only pic i could find online).