In reply to Reach>Talent:
Worth it? Yes for the instant dimming on looking down, but otherwise sometimes yes, sometimes no. My limited experience (2yrs weekly winter Nao only) is it all depends on what circumstances you are expecting to use it in and for, what your priorities are re light levels and time at that level, and the conditions and terrain you actually encounter.
Good in ideal clear situations of just looking up and down frequently in otherwise unobstructed landscape, but frustrating scanning with obstacles at different distances in the way, certain weather conditions and even clear cold still evenings where your out breath dims the head torch with every breath.
Mist, snow, heavy rain, obstacles particularly those that bounce back light, all can cause problems. They can be really bad in bad weather and can be a lot worse IMO than a standard head torch. Many situations better with non reactive mode. There is also a noticable delay in reacting with my Nao from dim to bright - don't know if that is common.
Try before you buy is my advice. Would I buy again? They have their place, but no, and overall personally I think for a lot of variable circumstances a headtorch with a range of (manually) adjustable outputs is far better even if more "hassle" adjusting, and probably safer in highly variable conditions or situations you can't predict what you will encounter.
I am sure others will disagree, but that is my experience if it helps.