"Good battery life on the mid settings, which are plenty bright to walk with."
Yes. I got the H501, and I was experimenting with the light intensity one week ago today when I was crossing the Sierra Nevada by trail. After twenty miles or so that day, it was getting dark when I pulled out the headlamp. Although it was gratifying to see how bright the high intensity was, I knew that it was going to last for only a few hours. The medium intensity setting was plenty bright enough, and that is what I was using. The low intensity setting would have been plenty bright for camp chores or inside a tent.
Lots of gram weinies will choose a light that uses AAA batteries, simply because of the reduced weight. Also, lithium is lighter than alkaline or NiMH.