The light is brilliant, 4 options (fixed, brighter fixed, strobe, flashing) all of which are supremely bright. Don't worry that the unit itself is small, it's the led's that pump the light out.
Now then, the strap...
I bought this assuming the strap was an extra and there would also be the usual bracket included. No, it's strap only unfortunately.
The strap will fit round any post but to secure it you thread the end through a hole. It does not lock into position. I cannot see this strap stayinf locked in place during lengthy mountain bike rides. The vibrations, shocks coupled with mud and water lubricating it should see you lose it in a forest or hilltop pretty soon. This did not become an issue for me as the release clip for the light snapped off on its third use, while I was fitting/testing it. I have thus thrown the stupid strap away and now using a standard bracket for it. Much better.
This strap was a prime example of a pointless gimmick. I wish companies would just stick to tried and tested methods.
A good light and cheap considering it's rechargeable, but the fixing issues bring the score down.