Yeah, esbit is probably not a good thing for heat exchangers. They tend to burn a bit sooty and thus will reduce the efficiency. Add in that they don't produce a high heat and you get close to the same results, anyway.
If you have good efficiency with a stove, HE pots won't help much. They work by trapping *excess* heat and putting it back into the pot. There are no free rides.
Postive to negative is general flow patterns. If you can put your hand over a pot and lift it, chances are there is not enough heat lost to care wether the heat is being transfered through a heat exchanger, or, conduction along the bottom of the pot. Follow? I would allow *some* heat loss, because with none, it wouldn't work. We think of fuel as the only combustable, but in fact there are three parts: hexamine, oxygen, and inert components. During combustion, we typically reduce the general size of things. For example: Hydrogen + Oxygen -> Water. A LOT of Hydrogen and oxygen are needed to produce a teaspoon of water. The extra heat sort of drives fresh air into the burners, a primary burning component, and flushes away expended fuel. (Glossing over a lot.)
Or, think of it this way, if you want: The heat from the stove is transfered at the heat excanger, leaving the so called heated air, cool. Cool air does NOT transfer heat, if anything it will remove heat from the pot. Tall pots are more prone to this type of cooling than shorter wider pots. (Actually, thermodynamics dictates that both heating and cooling take place at the same time, but, I am glossing over this for simplicity...not that I remremem...uhh...ber that much from 45 year old class work.)