This the standard that I'll now judge any other "pocket flashlight". 2 standard AAA batteries, LED with good balance of brightness and battery longevity. I normally squeeze this into my shirt pocket next to my phone and pen. Comes in handy traveling to business locations (test labs, etc.) and to light up the back yard when raccoons, etc. are lurking about.
Sure there are brighter and smaller options out there, but AAA batteries are a dime a dozen so to speak and IMO this is just the right size -- could be used as a striking instrument for SD as well.
If you can think of a better 2 AAA affair let me know and I'll try it out and be pleasantly shocked if it is "better".