The P2 slide switch can't really turn on in your pocket unless it snags on something, or if the LED leads get smooshed inwards. And the P2 intrinsically has a momentary mode--just squeeze it. The Freedom is more water resistant, and its dimming feature is handy, as are its other features if you can remember how to use them. What can I say, I have a Freedom and have never been that crazy about it, so I carry a P2. YMMV.

The Arc AAA is a real nice light and I love mine, but for typical occasional keychain usage, it's never going to beat cheapo coin cell lights in terms of cost effectiveness. A 50 cent coin cell light can easily last for years.

Note: the Photon series lights with red leds use a fancy HP/Agilent led that's unusually bright as such things go (much brighter than the cheap Countycomm red-led lights). Good on them for using such a high class part, but if you want a dim red light for briefly checking a readout, it might not be what you want.

Well I have had 2 of the older inovas come apart on me, my Photon is still working.

The Photon 3 red is very bright. Mine still has the origenal battery and it is 3 years old. Should I change it know?
I do not like that the area to press for momentary lighting is so small. I can imagen this becomeing a problem if cold or weak.
Is a P2 a photon 2?

Yes, P2 means Photon II (my abbreviation). LRI likes to say Photon I, Photon II, and Photon 3 (roman numerals for 1 and 2, arabic numeral for 3). I don't know why.

If your Photon is still bright, I don't see much need to change the battery, especially if you haven't been using it a lot.

I've never been that crazy about the P3. The Freedom really is an improvement, if you want a dimmable light. The P2 is still my favorite because of its simplicity, but I'm sort of a throwback.