I bought an NEI years ago and used it a bit, I never had it fail, but sometimes it would switch modes on me because of the way they designed the interface. I'd wind up trying to find something in a vehicle in the low mode, and instead having it strobe at me killing any sense of night vision i might have had. Or it would do the opposite mode switching and wind up ramping my low mode up to the high mode. Just too much hassle for an EDC.
I still use it, with a Surefire F04 beam shaper, with the head unscrewed a full turn, on the lowest mode, as a bedside reading light and for when nature calls in the early morning. As a battery vampire in its lowest mode, it does work very, very well. I'll just never use it on high again.