Of all the SF LED heads, KL1-6 and I have the lot, the one that always impresses me the most is the KL5. Don't know whether it's just the one I have, but it is just the brightest, whitest thing I've seen. The KL6 does have a bit more throw and allows up to 3 or 4 cells which helps run-time, but that KL5 is just a nice size, perfectly defined white circle of light and dead bright.
I've used it on either an M2 or on an E2 with an E2C which makes it much more pocketable...
I have a 'power failure' KL3 on a C3 body for 7+ hours run-time, but it is not anywhere near the brightness of the KL5.
Awesome head. But I would echo the comments about having heat dissipation - my KL5/M2 combo runs almost too hot to handle after not very many minutes.
kind regards,
Simon