As long as you aren't stuck with one battery, I would definitely want to carry a couple spares for that one.
That is the issue - the battery is internal and not replaceable. Once it's dead in the field that's it until you can find a USB charging source. Real shame in my opinion. Perhaps they did that to keep people from being able to put lousy cells in it and blame failures on the light itself. As a cave explorer this is unacceptable, as I plan to go through several sets of batteries in one day and for a long trip into the wilderness or even a weekend of remote caving this light would be basically useless. You could recharge it overnight with a separate mobile USB charging source (I have a cheap plastic box that holds two 18650s and has a USB port for charging things) but that's still pretty limited. Even as a backup headlamp it seems less than ideal this way.
Here's hoping they make a version that allows swappable cylindrical cells.
I have had one of these for several months and my only two negatives are that it didn't come with a top strap and that it doesn't have a removable battery.
I agree that wearing it too long it does end up bothering your head. That happened to me a while ago cleaning the basement i had it on an hour or so and my forehead was aching. aside from the top strap i would like more of a cushion then the one they give you.
This is actually a disturbing trend I've seen in some new headlamps using a proprietary, non-removable rechargeable batteries. The light and motion Solite, some of the new Petzl's etc. If you are taking a trip somewhere out of the way and extreme you can't be stuck with one battery you can't replace and you have no option for using it with disposable batteries. Considering Surefire's roots it's really sad they would at least not offer a platform where you can either replace the rechargeable battery or run it off a separate battery pack or with CR123s. For a light I use around the house, or car camping that's fine, anything else I better be able to at the very least carry spare rechargeable battery packs for, especially at this price point.
A second is how Surefire rates their lights, the 500 lumen maximus while impressive when I played with it at the shot show, the specs say it runs for 1 hour but Surefire's rating that for when the beam drops to 50 lumens. Now on a 100 lumen light I don't mind rating it's run time when it hits 50 lumens, but on a 500 lumen light calling it's run time when it's lost 90% of it's brightness is padding the specs pretty nicely, even though they do say what their criteria is. They should be using a % of original brightness not a raw lumen number, especially now that their lights vary a huge amount in lumens.
I do really like the completely adjustable output, and if they offered a replaceable rechargeable battery, a better head strap, I'd be tempted. I rarely need 500 lumens in a head lamp, but if it had really long run times at say 100 lumens compared to other options out there I'd be tempted.
If you can excuse an equally 'Olde Fart' of an Englishman what the heck are 'Yoddle-puppies'? I'm assuming that they are wild dogs or something similar but otherwise I'm not familiar with the term.