Most LED headlamps have an on/off switch and maybe a couple of intensity settings. The XP2 has an entire desktop utility that allows you to tweak the trade-off between beam intensity and burn time from the lamp's high- and low-output LEDs. Crank it up for maximum safety during a nighttime run, or drop it to preserve the battery for a long hike from base camp. The internal USB-rechargeable lithium-ion cell is backed up by a compartment for three AAAs.
WIRED Flip-up lens for focusing the beam.
TIRED Extra battery compartment adds bulk. A $20 headlamp would be plenty for most casual users.