Took my H600w caving with me for the first time today. I am 100% satisfied with its performance underground. I am glad I went with the neutral white version as the color quality of the LED is excellent (see picture at bottom). $89 well spent.
When I first took the light out of the box and turned it on I was concerned there wasn't enough spill for my liking, and that it would be harder to see things in my peripheral vision. However, when I placed it on my head the spill did not seem too narrow at all. I was also concerned that the spill would be so dim and useless on the lower settings and that the hotspot would be the only usable portion of the beam, but I am happy to report that the beam is still plenty wide enough in even the lowest setting.
The size of the hotspot is perfect for my needs and not too concentrated. As a result it doesn't throw very far (although farther than most), but I wasn't looking for a thrower anyway. It does put out a massive wall of light though on turbo mode, which is ideal for lighting up entire cave rooms. As a caver, it's usually very hard to find a light that does this well. There are plenty of lights that can throw very far and plenty of lights that are super diffuse for wide lighting, but the H600w seems to be one of the very few with the ability to strike a happy medium.
The lower of the two middle settings (18 lumens) seemed to be the brightness setting I used most often and was more than enough light. Zebra claims 50 hours of runtime on this setting with a 2900mAh battery, which isn't too shabby for a single cell caving light.
No problems with operating the switch. Even with gloves on it is easy to find and depress it.
My helmet is a lot lighter now using this light. I am still amazed at how lightweight the H600w is. I am also very happy that there is no longer a battery pack or power cord on my helmet to constantly snag on things.
As a final note, I took my dirty H600w and ran it under the faucet after my caving trip. Not all the dirt came off, so I took an old toothbrush to it while water was still running onto it. Taking it one step further I placed my light in the sink and filled it with water, allowing it sit fully immersed for over five full minutes. During this time of total immersion I operated the switch and used the toothbrush on it again at the tailcap, lens and switch areas just for good measure. I then took it out of the water and let it run the full three minutes of turbo (where the light gets very hot). No condensation whatsoever formed on the lens throughout the entire test, and when I took the tailcap off not a single drop of water was inside. I think it's safe to say this light is as waterproof as I'll ever need it to be. : )
Here is a picture where I used the H600w for light painting on turbo mode:
(note that the light is not this bright in real life, it just looks this way because of the 8 second exposure setting)
Apparently 645 lumens was overkill, so I brought it down to to 56 lumen setting and got a much better result: