I have a drop in conversion on a G2 Nitrolon. It lives on an AR surefire mount. It has stood up to a lot of rounds downrange and still works fine. It's also a good illuminator and seems to do as good a job as the white LED light on my Streamlight TLR-2 (which I also like a lot).
I have another G2 which came as an LED model from the beginning. That G2 LED also lives on an AR and has also withstood a lot of pounding.
Maybe the Fenix might be a nice belt flashlight. I'm not sure the Fenix would be usable as a weapon light. I've had a few "high tech miracle flashlights" made in China. a couple have worked out, most died early deaths and went into the trash can.
If it's just to be used as a belt flashlight Fenix might be ok. However I have learned that focus of the flashlight beam is as important as lumens. I have a 120 lumen white LED flashlight which has a broader beam than my G2 LED, and even if it produces 50% more lumens, the G2 makes a hotter, brighter, whiter beam. This is important for a weapon light or a tactical light, in which the tighter beam has a better dazzle effect on your opponent.
I have never tried the Fenix. but I know the G2 LED is capable of tactical-dazzle use. BTW there is also a G2Z model shaped for using the "Surefire Method" for using a tactical light with handgun.