What is the practical experience question?
First of all, as a space heater, forget it. Second, you would not want to burn Esbit in a confined space. It takes a lot of energy to heat up a volume like a tent. Unfortunately, Esbit is not much good if you are outside in a wind.
You are much better off using the Esbit to heat a cup or two of water. Besides, that is as much as it is good for, heat-wise. Once your water is hot, you drink it. You will get more effect out of that taken internally than just trying to warm air around you.
Esbit is kind of expensive for anything except using it to heat a cup or two of water. It is very practical to have a few cubes of it hidden away in some winter emergency kit, along with your titanium cup and a lighter.