Well for a long time now I've carried this light, the Surefire C2. I can't really complain too much about it. I've used it three times while stranded in rural Arkansas and believe me having this thing in your pocket really comes in handy.
Well like I said I've been pretty happy with it and I've gotten my money's worth. The only thing I really didn't like about it was that the runtime is really poor. Oh it'll give you an hour's worth of light all right but the super bright light you want runs out pretty fast. I've also longed for an LED.
Surefire makes their own 5W LED coversion kit for it for $140! $140! Honestly, screw that. Screw that big time.
I thought about another light but there was always something wrong with it. I like the size and feel of the C2, I like the lockout tailcap, etc. etc.
So I thought I was stuck. Then I found out about this wonderful product.
How do I know it's any good? Well I've come to trust this source very much. They've never been wrong and it's a purely unbiased well informed source.
You don't lose very much of the light's output and in return you get a regulated circuit. For you non light junkies, that basically means this circuit drains the battery uniformly so it's the same brightness from beginning to end. Comparing the tests on FlashlightReviews.com confirmed my experiences: the standard C2 is plenty bright but it drains very quickly. The regulated circuitry on this head seems to give it a lot of consistency and adds a hair of total runtime.
I've ordered one. I think it should be a worthy addition to my everyday carry.