I see these are currently on offer on on one for £50.
Does anyone have one of these? Are they any good and can they be run from a USB external power pack like the Anker 15000mah packs?

There's one here for £40...
http://www.jejamescycles.co.uk/niteride ... wgodr2EAyw

As for how good, sorry don't know!

I had an old version, very small and nice to use, was a shame it packed up after 18 months (as did my hope light), now on exposures (2 years) and been trouble free