I'm a volunteer firefighter and my whole city uses Underwater Kinetics UK 4AAs. Pretty much all of us are still using the Xenon lamps only one guy has the LED version. I haven't seen this light compared to the Xenons so I can't comment on it.
The Xenons have a tight beam that's pretty good at cutting through smoke, but it's not useful for general lighting purposes as it has practically no usable spill. The beam is also not very smooth, but works well for use in smoke.
There' a version that switch on by twisting the bezel and also one that has a clickie switch in addition to the bezel twist option. You can get lights with different safety ratings.
The light is supposed to be run on primaries and not on rechargables. The reason for this is that the safety rating is granted only for use with primaries.
Rechargables do work in this light, although some are a bit too short, so the rattle around and will lose contact with the lamp assembly. I'm only using rechargables on the one light that I don't put on my helmet.
There used to be a rechargable version of this light, but I can't find it on their web site right now. It has a slightly higher output that the normal one.
You can put this higher output lamp assembly in a normal non-rechargeble light, but again you'll lose the safety rating.
There are tons of helmet mounts for specific types of helmets available as well as generic ones.
Also you can get an accesory to convert it to an angle head light.
The alkaline version is supposed to run 4 hours on a set of batteries.
As for durability of the light, we have about 100 guys using these lights since 2003 and I'm not aware that one of them has failed, yet. They've gone into countless burning buildungs and none of them have melted or anything. They also get knocked around quite a bit on the helmet and I haven't had a bulb break, yet (not sure about everybody else, but definitely not in my station). The bulb is supposed to last 11 hours, if I remember correctly, but I've run quite a few sets of batteries through mine and I'm still using the original bulb that came with the lamp and it's still as bright as on the first day.
The newer LED versions have a higher lumes rating and are focusable, but as I stated above I've never tried one.
There's also a new series of lights from Pila (here in Germany distributed by Parat) the PX1 that use the same 4AA form factor (they fit in the same helmet mounts) and can be had with either a Xenon bulb or with "White" or "Amber" LEDs. But again I've never seen one of these light so I can't comment on them.
The biggest drawback is that the UKs don't have a battery indicator function, so you never know how much juice is left before the output drops down.
I hope this helps you in your search.
Markus