Saw this review on road.cc of essentially a modern bottle/rim dynamo:
https://road.cc/content/review/pedalcel ... rce-284273

It's a good review - seems to suggest overall price similar to a dynamo hub/battery, higher current output, works better at low (off-road?) speeds and easily swapped between bikes...

Anyone tried one?

Looks similar to the Velogical rim dynamo that has been around for a few years.
http://www.velogical-engineering.com/ve ... -efficient

It's a good review - seems to suggest overall price similar to a dynamo hub/battery, higher current output, works better at low (off-road?) speeds and easily swapped between bikes...

They do work well at low speed but bear in mind that 'off-road' can be their downfall as it's often muddier / wetter.