I have an L5 and I like it a lot. I run it on one 17670 rechargable Li-ion battery, which makes running cost nil. I also have an L6, which is quite a bit larger, and the L5 has a better beam pattern and seems to me a bit brighter.
I am not sure of the history of why the L5 was developed, but I believe that it was intended as a combat or police duty light. It is certainly well made and gives the impression of being sturdy. That is an important quality in a light to me.
If you are a person who is sensitive to size, then the comments about the size of the L5 head will be important. To me, on the other hand, the L5 is not that much bigger than a 6P. It is bigger, but the difference doesnt make a difference -- at least to me.
In terms of cost, although the L5 is more expensive than any number of other possibilities, I regard it as cheap, because to get similar service from another LED light, I think you would normally have to go to a custom light, which would be more expensive still.
bill lafferty