I am carrying the 580 lumen version of the XT2C as I type this, and I like the light every much. The user interface is the best I have seen for the purpose of this light, and the ability to use 18650 means I can use the light as much as I want without worrying about cost. Outdoors, I can illuminate areas that are quite some distance away. My light has survived some unintentional drop tests onto various surfaces, including concrete, from 3 feet without issues. Runtime using CR123 is considerably shorter, so anyone getting one of these lights should definitely plan on using 18650.
There has been some discussion about how Klarus could have managed an increase in output with even a bigger increase in run time with just a change to a later generation of the same LED. It is entirely possible that they were able to use a higher capacity 18650 to get those numbers. I would love to see an output v. runtime graph for the high setting, and would likely upgrade to this light if it has a reasonably flat and horizontal curve.