I have not used esbit for cooking, but I have used them for running model steam engines. Esbit smells nasty and leaves a residue after burning - although it burns really hot, and the tabs take up little space.

On the other hand sterno doesn't smell bad (to me anyway) and the mess is left in the can. The big benefit to sterno I think would be that a can will burn a very long time, and the flame area is larger (dependent on the can size) - it's also more readily available most places.