dd,

I'm thinking the dimensions given might not be accurate, either that or the tube described as being actual size is not accurate.

My thought was that you'd add boiling water to a zip lock bag with filtered water for a warm drink of your choice. I'm thinking you could boil a few ounces of water with just a candle/fire cube.

Not really for cooking, more for making a warming drink/bullion in a pinch. Might not even be practical, but I like the idea and will be buying one in each size before my next trip.
I figure I'll find a good use for them.
I also will be buying the aluminum box with folding handle and the stainless box with latches. I'll make a waterproof gasket out of silicone for that and will work it into my outdoor gear somewhere.