personally, I'm more concerned with theft.
I'm a fireman, and if (I realize this can be a big IF) you live in an area with a FD with a fast response time, the heat is not really a huge issue. You may have smoke issues, and that can be serious, yes.
I have mine in a room with an exterior wall and window, so whomever can get water on the box if needed without much hassle. But, I live in a neighborhood, with a hydrant across the street, and a professionally manned fire station 8 blocks away.
We all have different challenges to deal with. Each challenge comes with it's own benefit.
Its a novel design, but I keep more than just guns in mine. The door is the large enough to let plenty of light inside, and I don't need power of any kind to operate my safe.
Gotta love good old American Ingenuity, If there is demand (clearly there is), free market will provide an option.
PE