I prototyped 8-12 of these in my garage and tested them in my backyard last winter.
They are, as a class, very efficient and run very hot. Probably will be regulated in the US under the recently proposed new EPA regs, there were previously exempted as stoves with and air:fuel ratio in excess of 50:1 by weight. If you are going to bring one inside the house, definitely plan on using an outside air intake, or cold air intake or whatever you want to call it, don't feed it warm air from inside the house cause it is going to suck you dry.
There is a .pdf about rocket stoves that has all the math worked out for a first time builder. The .pdf is about US$15, widely available from multiple links on
www.permies.com and absolutely worth the money to save repeating mistakes that have already been made. Critical dimension is throat diameter. Once you pick a throat diameter the length and diameter of the vertical feed down tube is plug and chug, same for the diameter and height of the vertical exhaust.
Supposedly throat diameters at and under 4" are "finicky". I spent a bunch of time on a 3 5/8" throat diameter stove last winter. It could be a good size for a cottage around 1200sqft with good airseals and good insulation. To get it running I had to feed it bone dry wood split to about the size of my pinky finger, maybe 1/2" (1cm) in diameter. "Zero rocket stove" should hit on google.
That SOB was finicky on a good day and higher maintenance than a Hollywood starlet on the other days. I finally got it hot enough to really take off and go "whooooooosh" instead of just roaring, one time. I just don't have access to wood with straight enough grain to split enough wood small enough to feed that thing.
My 6" throat diameter prototypes did a lot better, but I was still feeding them wood about the size of a 2x2 split in half. Maybe 1x2 or 1x3cm. Ridiculously small splits.
The other short coming, as already anticipated by coldfront, is most of the heat from a rocket stove is in the exhaust gas. Certainly they run good cold and much better when the material of the stove is hot; but even then most of the generated heat is in the exhaust gas and needs some kind of masonry or adobe heatsink to be captured.
Primary tuning difficulty is ash production. As ash builds up at the first corner where the vertical feed meets the horizontal throat, the critical dimension - throat diameter- changes, and changes for the worse. If you feed them too much wood ash builds up quick and the stove gets sluggish, which leads to more ash build up, then it drops out of secondary burn and eventually the fool thing just stalls, smoking up your living room.
Rockets are a great idea and someone is going to make a million dollars on them when they get it figured out. In the meantime I'll stick with my catalytic equipped Blaze King, feed it big gnarly knotty chunks that can't be split under 8" max dimension and play with rockets in the back garden as a hobby. A properly sized masonry heater with a modern design that supports secondary combustion is much better understood beast for now.
Don't mean to sound discouraging OP. try googling up 'P-channel" or "Peter Channel", should take you to another guy, in the Netherlands no less, who is fooling with rockets because there are so few trees in Holland. He is heating quite a few square feet of house with just busted up shipping pallets.