I've started mounting my bike lights via shock cord.
The previously mentioned Orfos Pro LED flares ship with Velcro One-Wrap for mounting. This works well enough, but lately I’ve decided I prefer using shock cord and cord locks. The cordlocks add a little weight to the system, but this setup mounts to all the things I want to mount the lights to, and makes it very easy to tighten. After tightening the lights don’t move around at all, where with the Velcro they would move a little on a bumpy road. This system is also quick to attach and detach, which I appreciate when parking, and can be more easily manipulated when wearing full-fingered gloves.
