You wont have any trouble with water or fire. All you need more is a safe place to hide it. It isn't that big so you could hide it anywhere you want.
I would not say no problem with fire. It seems that if a long fire hits it that metal might have some issues. It looks like a slim card like metal slab.
So I would predict at a certain point it would burn/char. But yes it's better then a piece of paper for sure.
I`d say keep all your precious stuff in a metal box.
If the house catches fire, you grab it and run out. Or just leave it there, since it wont burn down like the rest of the house.
The metal card in a fire-retardant safe would not be a bad bet and fairly easy to find. Otherwise, i'm not sure. The card would not melt but the ink on it would and the metal would be dark and singed, so possibly erasing the information on it one way or another?
Regardless, i think you should engrave a very valuable key on metal, and then put it somewhere fire cant really destroy it, like in a safe or in the basement somewhere fire can't get around.