Based on Amazon reviews, it looks pretty much like bullshit. I mean, it works, but it doesn't really "run on water", the fuel cell needs to be replaced after enough uses, the "25-year shelf life" refers to how long the fuel cell stays good for if you haven't dipped it in water yet, and the flashlight isn't very bright.

https://www.amazon.com/Hydralight-Flashlight-Batteries-Emergency-Hurricane/dp/B076JJSJ97