I have two of them. I don't have a Photon III.
Brightness compared to my other 2016 keychain lights is equal in brightest level, and the other levels are good if less is needed. The strobe speeds are fine, slow and fast. Starts on high, next press is medium level, next is low level, next is slow strobe, next is fast strobe, next is off. If you wait around 2 seconds after pressing the button (on whatever mode you're on), it will turn off. So you won't have to cycle through the other modes before it goes off.
I haven't changed batteries yet, so don't have the scoop on that. Looks to be easier than the Photon and probably even the Inova. I'm sure water resistance should be same after change.
The main light part attaches and comes off the clip with a noticable 'click' so you know it's happened. It fastens on pretty tight. In the pocket, it feels good since it is flat with rounded corners. I'm sure a pretty good bump on the leg could separate the clip from the light, along with the bruise on your leg.
There is a soft touch to the switch, that doesn't mean it would come on easy, but the switch feels good to me.
All in all, I really like the ones I have. I got one with a red case, and one with a blue case. It looks like anywhere you find them they're going to be about $15, but you'd want to get other stuff, because shipping will be added on. If you wanted to try one of mine, I could save you the shipping charge, at least. Both of mine are new. Search on Google or whereever, perhaps you could find them cheaper, but from what I found, $15 + shipping is what they're going for.