Hi. I'm a park ranger in New Hampshire and use lots of headlights for SAR. DON'T BUY THE MYO. I returned it- the whole thing is hard to figure out in terms of which brightness you are on in the LED part, especially when you are as you often are somewhat hypothermic.
the PT Yukon is a far better light. Actually for most purposes their lighter and much simpler Matrix 2 is fine, the Yukon being somewhat brighter. If you are into trail running or Search and Rescue, one of the Niterider products or the far more expensive Lupine Edison headlight are needed, although I have to say I can move pretty fast with dark adapted eyes, as I did the night before last, with just the Matrix 2, when the snow is on the ground and conditions are just right. I would have to say that the ultimate combo, if you don't want to spend the money on a Niterider, which I don't recommend, or a Lupine, which is really meant for nite-bikers and SAR, is the following:
a. a Matrix 2- very easy to use, 2 batts, bright spot
b. a Petzl Tikka Plus (so our Petzl rep won't kill me over what I said about the Myo, just kidding) more of a flood and long battery life.
You can put them both on very easily- no over the head strap to untangle, just around the head. One, the Matrix, on top for views ahead of you on the trail, and two, the Tikka, pointing down, to light up your trail right ahead of your feet. That's unbeatable and has the advantage that both are LEDs, both have long lives, and the Tikka even after the night is over can carry on with slightly less light if you are going into your second night without replacement batteries for some reason.
I used an older Tikka on a climb to 20,000 feet in the Andes a few years ago. It was just fine. Turned it on when leaving the tent at 11pm, and lit up the glacier ahead of me just fine until twilight at 6am. Funny thing was, I FORGOT TO TURN OFF THE LIGHT. The next night I went out for a second attempt, and noticed that it was still turned on, strapped across my helmet. It looked bright enough and the nearest AAA batteries were who knows where, so I just said to heck with it and climbed again and no problems, it lit up the crevasses, climbing route, etc. I turned it off when I realized it was still on after coming back at 10am. Still used it until I got to a town that had AAAs for a few more days but didn't climb on it. POINT: Great backup all purpose light, the Tikka, and I assume the Tikka Plus as well.