On the other hand, while rocket stoves burn very hot and very clean, they are not efficient. Rocket stoves are hungry and consume lots of fuel."
If Kimberly stoves were so efficient, they would include a graph from a Testo 330 gas analyzer (or something similar) on their website; do they? They
are really nice looking. It is also interesting that Kimberly is even comparing themselves to a rocket stove.
It would not be possible to burn clean and not efficiently. Burning fast and hot
necessarily make the burn more efficient. What this person may be referring to is that a j-tube design creates a lot of heat, so you need to store it somewhere or your living environment will alternate between too hot and too cold as a cast iron stove does.
There lies the intersection of the rocket mass heater and masonry heater. Both of them have relatively small combustion areas and a large mass in which to store the heat.
Building a rocket design with a lot of metal parts would not tell you whether you would like a rocket mass heater in your house. Metal does not have good thermal storage characteristics.
People who have rocket mass heaters in their living quarters (including me) are very happy with how much heat they get for the amount of wood consumed.