I keep a Pelican 2130 Mini Flasher clipped to my kayaking PFD. It's not super bright, but works as advertised, and is small and light enough. Haven't tested it's burn time, but Pelican claims 130 hrs.
In my opinion Pelican could have made the unit a bit brighter. Mabey by replacing the red lens with a clear one?? I have talked to them about this in the past, but no changes yet. They already have the clear lens in use on the infrared mini flasher. Just my 2 cents.
I used one for few weeks, too weak. You want to get a Grace Ind. LED firefighter/diver flasher. It has three LEDs, and comes in many color combinations. I carry a red/white/blue on my gear. Also it has a d-ring and a locking clothing clip.