Let me start with this: I'm not a caver. My life will never depend on my back up light working. When my primary light goes out (rarely these days) its merely an inconvenience.
I don't need it to be good to 900 feet.
I want it to be black. Preferably not metal cased, as it will get scratched and ignored most of its life.
That said, I've been diving Photon Torpedos forever - at least 6 or 7 years. Upgraded them to LED when that became an option. I sold one awhile back, as I don't need two back up's. My primary back up (that's fun to say) is now a bit long in the tooth, a bit crunchy and I'm looking for something else.
Its a back up - I don't need a 10 watt flame thrower disguised as a 3C or 4AA back up. Bright is nice. Long lasting is nice. Reliable is a must. I want to put batteries in it, and forget about it until the time change, when I replace its batts (like I do in my Smoke detectors.)
2C size is better for me, as I'm not tall. I won't buy something that doesn't use AA or C batts. I have no time and no inclination to buy some wacky batt I can't find at a 711.
Lighting has come a LONG way in 6 or 7 years. What's the Shiz today?