The SF KL3 (gen-2) is a nifty "lego" combo on any C2/C3/M2/Z2 body variant.
You should be aware, however, that the "4.25 + 4.75 hrs." runtime specified for the KL3 on Surefire's website is, um, incorrect. Like many manufacturers, their website is often out-of-date in certain respects. In this case, THAT runtime applies (accurately) to the OLD (gen-1) KL3 LED head -- which was very much a long-running "flooder," kinda like an Inova X5 on steroids. It's a nice light for night walks/hikes, but it's out of production.
The new KL3 versions, however, are very much the narrow-beamed throwers -- with the 3 1/2 hr. runtime (to 50%) as accurately indicated in the fine FLReviews.com analysis. That's still a pretty decent runtime.
Gen-1... gen-2... gen-2.5... schmen-2. Confusing, eh?