I haven't used a Kandle but I really like the Mighty Bright TravelFlex, it's brighter than the M-Edge light. It is also bigger but still very portable. I have an M-Edge and a BookArmour case and with both I can clip the TravelFlex on the spine.
If I use it every day both the TravelFlex and the M-Edge light last me a week (both use 1AAA battery). In my opinion the TravelFlex has a better build quality than the M-Edge.