I own and have used this light regularly as a backup since I first got one. However today LRI makes tiny keychain lights with infinite brightness settings for around $10. They use cr2016 batteries, are much brighter than the Photon Pro and the beam is much smoother.
Mine has an electronic switch and a stated run time of 12 hours. I like to keep it clipped to the sheath of whatever I am carrying.
Sorry I am lost here or is it I am that tired. The Pro uses 1 x AA. I have two Pro's, 1 x REX (which is a great light albiet low run time) and 5 x standard model 1 Photons and 1 x Freedom. None of the CR2016 or 2032 lights are as bright as the Pro. I think for keychain lights (miniaturised) you cannot beat a Photon Freedom. But as much as I like the Pro the switch is a little to hard to locate so I was happy when I got my Zebra light SC51. I will say however that Photon has a lifetime warranty on all products and I have tested that with 2 issues and there were no questions asked. Their customer service and desire to help customers is second to none and probably the best there is.