One tablet will boil a gallon of water easily.
One gallon? Interesting, according to the Esbit website one tablet will only bring 400mL of water to a boil.
Can we see pictures of your magic hexamine stove?
The British army hexamine tab weighs 245 grams (actually there is 8 separate tablets in a waxed paper box)
Each Esbit weighs 14 grams and can boil 400ml, so taking into account the box, the tablets weigh around 200 grams
Therefore 200/14 * 400 = 5.7 litres or just over 1 gallon if we take into consideration that Esbits may have a slightly higher heat output.
The British army waxed cardboard Hexamine tablet is sized to fit perfectly into a folded up British Army Hexamine stove. This helps protect the fuel inside.
There is quite a good source of info on solid fuel stoves at
http://zenstoves.net/SolidFuelBurner.htmFrom the zenstoves website
Not all fuel tabs are created equal. Although the many different brands of Hexamine share the same main ingredient, they vary in quality and may use different binding agents.