I was recently faced with the same dilemma about a headlamp. I quickly decided on 18650's, as they are functionally lighter per lumen-hour than any other battery format available in a headlamp, and even more-so on longer trips when combined with a good light-weight solar panel and charger, especially if you run the numbers on NCR18650B's. Sure you could go caving or back-packing with a 1XAAA headlamp and run it at 5 lumens or less all the time, and have a much lighter weight solution, but that sort of minimalism isn't something I'm interested in. Far as I'm concerned, that sort of "extreme" minimalism (ultra-light-weight-packing) has consequences in terms of safety and security for when things don't go as planned. A good 18650 powered headlamp can offer hours and hours of sustained output bright enough to safely navigate/climb a gnarly chimney in a cave. The warm tint available on some of the nicer options is more useful in earthy environments than the typical cool white found on most AAA powered headlamps, and those warmer tints offered on armytek especially can also be a useful source of psychological comfort when you are in the middle of a long tight crawl while caving, and begin to feel the anxiety/claustrophobia set in. A bright warm tinted light can instantly make that tight tube feel a little less restrictive.
In my quest for the ultimate 18650 headlamp the list started off pretty long, with options from Spark, NiteCore, Jetbeam, Fenix, Skilhunt, Armytek, and Zebralight.
No doubt, if you've spent some time comparing the basic stats of all of the various options from these brands (and perhaps more), it probably didn't take too long to narrow it down to the Zebralight or Armytek options, For me it came down to the Zebralight H600Fw MKII vs Armytek Wizard Pro V2 Warm. They offer the warmer tinted neutral's, Properly floody beam patterns for headlamp usage, lots of efficient low modes that run for a really long time, and less weight than competing products by a fair margin. (the zebralight is insanely light weight for an 18650 powered device).
From there the decision is difficult, as both of these directions have strong points. I don't think there's really a "wrong" answer here.
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I ultimately decided on and received 2 Wizard Pro V2 Warm's a few weeks ago and have been using them at every opportunity to give them a thorough workout before trusting them in the back-country.
I've been performing electrical testing of the Wizards, and found that many of the modes are a bit lower output and a bit longer running than specified.
I estimate the modes for the warm edition V2 Pro to be closer to the following:
FF1:~0.19 lumen OTF for ~6 months on an NCR18650B.
FF2: ~2.2 lumen OTF for ~27.5 days on an NCR18650B.
FF3: ~8 lumen OTF for ~8.5 days on an NCR18650B.
MM1: ~55 lumen OTF for ~31.5 hours on an NCR18650B.
MM2: ~145 lumen OTF for ~11.5 hours on an NCR18650B.
MM3: ~325 lumen OTF for ~4.4 hours on an NCR18650B.
MAX: ~765 lumen OTF for ~1.1 hour on an NCR18650B (accumulated)
I did a run-time test on MM3 and it ran solid for 4 hours and 30 minutes. I also double checked my readings with a friends high end Fluke true RMS DMM. The unit draws power "cleanly" in all modes (no meaningful duty-cycle or "AC" input). This is a good thing, as it means the power is drawn from the battery in the most efficient possible manner. Tail-cap measurements should be pretty useful to estimate runtime on these lights, since there is no "weird" power draw that an ordinary DMM can't resolve. I will eventually try to test MM2 and MM1 to confirm the estimates from tests.
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From a practical standpoint, the key differences in actual use between the H600Fw MK II and the Wizard Pro V2 are going to come down to UI and beam pattern. I think that for most people, the differences in weight, tint options, implied durability, indication systems, etc, would be largely academic and non-issues in actual implementation.
In reading about, and looking at reviews and beamshots of as many of these lights (or similar) that I could find, and including some of my own experience in the process, the Wizard stood out as having a subjectively preferable method of both controlling modes (UI), and distributing lumens (beam pattern via TIR optic). My biggest concern with any sort of "diffuser" lens (as found on the H600F) is that they are high-glare for onlookers, even from steep angles, where a TIR optic provides more rigid control of light, and should also be more efficient, both in terms emitter to OTF, but also in terms of simply making better use of those lumens (less unnecessarily wide "scatter" flood).
Having used the Wizards now for a few weeks, I would have to say that the UI and TIR optics are indeed what I was hoping for. The beam pattern is for all intents and purposes, a controlled "splotch" of light with diffuse edges of rapidly diminishing lux outside of the beam-proper. What this means, is that I can place a nice splotch of light on for instance, the "camp kitchen," without "blinding" other members of my party who may be busy with other tasks of their own.
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I paid $85 each for my Wizard Pro V2's from illumn dot com with the CPF discount.