In the upper midwest an energy efficient 4500 sq ft house one will require 100 MBTU over the course of a winter if the average temperature raise is 50F. Wood contains at most 30 MBTU per cord if perfect, dry, and no loss (which does not happen)
So a 100% efficient system in that situation would consume a little more than 3 cords.
Rocket Mass Heater is not going to invent heat. Further, there were no building codes for it when I built the house. A quick check says there still are no building codes addressing the design which is not a trivial point. Even further, the exhaust gas is very low temp, which means there is a CO danger.
I like the theory of the design which is why I have a Tulikivi. It weights 15 ton which is kept about 110F radiating, 90% efficient if I run it correctly, and does not have the nasty flue issues. And I have the bake oven which makes the best pizza and bread.