You really can't compare the Ion to any other light, simply because of it's floody beam. I really like the flood for my keychain light, since floods are much more useful up close. Most of the time I stick on low, but high is quite nice for lighting up an entire room. I've had mine since February, and I'm only on my second battery (CR2 primary). Keep in mind this included
a lot of playing around with on the first battery, so under "normal use", it would last even longer.
It works on rechargables, but if you plan on using them, get the
Ion kit. It clears up any shakey, flickery output when using it on low, and allows use on high. With AW's RCR2s, you'll need a spacer (which the kit comes with) of some sort (I originally used aluminum foil, but this caused flickering) to be able to activate the high level. The battery is just too short otherwise, and the head turns fully down without hitting high. On low with a RCR2, it's much, much brighter than the low with a CR2 primary. High is only marginally brighter. Expect 2.5-3.5 hours of good, useful light on low with an RCR2. You probably won't even bother with the High level, so runtime on High might not be worth worrying about.
I really like my Ion, but my customized Jil Intelli might kick it off the keychain, as might an Exolion if I can pick up another one. If they don't replace my Ion, I'm seriously considering getting an aluminum bodied one (probably blue), since the aluminum bronze one really is quite heavy. I didn't think it would matter much, but if I switch it with my Jil, I can really feel the difference in my pocket.