Rating: 4 / 5
I picked up a Firefly a couple weeks ago on a whim. I figured it would be a fun toy, and maybe make the one Lexan bottle I carry a bit more multi purpose.
I tried it out recently. (it was used on a standard Nalgene bottle, a light blue color.)
The attachment was simple enough, and fits better than the original lid in some ways.
It does take a bit of getting used to the very, very tiny button that turns it on and off.
In its testing recently, it worked about how I figured it would. As a light for walking, no, this DOES NOT work! It is too highly diffused.
But for in your tent? It works great. Going thru the water it is a soft, gentle light. It lights up your tent, but isn't harsh. I could see everything in my tent last night, but never had night blindness after turning the light off. The blue color of my bottle helped, it colored the water. One thing I hate about most LED's is how harsh the light is. Reading with it was easy, as it was next to me on the tent floor. Easier than having my headlamp on.
I have a feeling my son is going to love it for when he is in the tent before me. It lighting up the whole tent with warmth will make him happy. In the past I have often had to rig up a headlamp on the ceiling of the tent with a biner, that barely lit up our Quarterdome.
We also used the lantern outside, and had it upside down. Put out a decent amount of light on our table.