The fenix has a circuit in it that keeps the light bright as the battery runs down. However, the Romisen is fine for a kid. Leave it on the bike, a helmet mounted light will get trashed when he tosses the helmet and if he does crash (more likely than an adult), the mounting may not allow the helmet to skid. With the electrical conduit clamps, the flashlight would be mounted securely and be no different than a bike specific light- except way cheaper and brighter.