In reply to fire_munki:
Looks excellent value, but whether it is sufficient illumination depends on how difficult the trails you plan to ride. You'll be fine on fire roads and the like, but I'd want a bit more for anything rocky or technical.
Personally I have a 2000 lumen light on my bars and 900 on my helmet - really useful to have both as often you need to look it a different direction to the way the bike is pointing!
However what you may find is that you can start off using this on your handlebars, and if you get into it (and it is fun) you can then get something brighter and use this on your helmet