I actually have this clamp:
http://dx.com/p/mount-holder-clip-clamp-for-bicycle-bike-led-light-lamp-flashlight-black-55828
I’ve used it briefly and it’s only suitable for the smaller lights like an Ultrafire 501b (P60 host?). The plastic part that mounts underneath the light is very flexible and flimsy, and the top part where the clamp swivels is flimsy and can actually be removed quite easily, I’d hate to think what would happen if you hit a big bump with a larger flashlight in it. Otherwise it’s a handy helmet clamp if used upside down reverse style with a small flashlight.
I have several clamps that I’m currently using, this one is by far the most stable:
http://www.dealextreme.com/p/universal-bicycle-mount-for-flashlights-and-gadgets-2cm-3cm-diameter-adjustable-15642?item=2
and works great with my trustfire TR-3T6. It’s not a quick realease style, but in a matter of seconds you can unscrew the screw with your hands and take the flashlight with you, you don’t need any tools. As I live in Vietnam leaving my bike unseen is not an option, and with this clamp I feel pretty safe, in particular as their are very skillful motorbike thieves prowling the roads.
If you’re using 26550 lights like the Shadow JMO7 pro this one works well:
http://www.dealextreme.com/p/universal-bicycle-mount-8274?item=16
I’ve bought this one from several places in Vietnam, and each one is a slightly different variant made of softer/harder plastics, ones that swivel %360 and ones that are fixed. They all work, the harder plastic versions are a bit more stable on the handle bars. It’s a lottery if you order it on the internet as to which one you will actually get, but they all provide more stability than this particular mount:
http://www.dealextreme.com/p/universal-bicycle-swivel-mount-for-flashlights-and-lasers-1-7-3-0cm-flexible-diameter-21314?item=20
which is perhaps the one you’re referring to or similar as it’s just a rubber style clamp and better suited for smaller lights as a helmet mount.
If you find the swivel version of the one I’ve posted above there is a better chance of getting the hard plastic version, although the soft ones still work fine with my JM07 and Poppas 878 26650 lights.
Which flashlight are you using?