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Reminder, an actual rocket stove will have its flue insulated. Those stoves that do not have an insulated flue are not rocket stoves. The insulation allows the flue gases to get hotter and burn cleaner. The flue also needs to be a certain minimal height or this effect does not work properly. This increases fuel efficiency, a great deal, and takes a normal stove into "rocket" stove territory. That being said, the fast updraft stoves that do not have insulation are still more fuel efficient than standard stove types. Most rocket stoves shown online are too short and/or are not insulated. One of the major flaws, for most of the designs even when insulated, is the lack of proper height. This misinformation is so common now that most people no longer know the difference and you will find "professionals" and various wiki with misinformation.
The difference between properly designed rocket stoves and improperly designed "rocket" stoves is as much as 40% fuel efficiency. Remember, though, even the improperly designed stoves will be about 15-20% better than open fires and a few % better than normal stoves.
