The Exposure Joystick is a fine little light, but it'll only last around 10 hours on the medium setting. I guess the best way to use it on a ride like the Dun Run or Exmouth Exodus is to use it on low when the local lighting is fine, and switch to one of the two higher settings when necessary. It's lifetime on the brightest setting is only 3 hours or so, but 24 on the dimmest.
I've got a triple piggyback cell to plug into mine, and that ups the lifetime to 12 hours on the brightest setting, and 96 on the dimmest! Buying a piggyback cell does however (i) increase the price substantially & (ii) somewhat defeat the CFD (Cable Free Design) aspect.
The Joystick is available with either a helmet mount or bar mount, but the bar mount option costs more. It is well designed and manufactured though.