weigh your bottles and subtract the weight of an empty bottle and write the fuel weight on the tank somewhere with a magic marker. Then you'll know how much you used - say 2.5 oz for a certain trip - next time take one with 2.5 oz of fuel left in it for the same or similar trip, then you start with less weight than full bottles.

However the two - esbit and pocket rocket are completely different machines and your specific usage will determine which to take, or whether to try something else. There is no one best solution for all usages... crazy
Jim thanks
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These are my own opinions based on wisdom earned through many wrong decisions. Your mileage may vary.