There's a few masons around the US that do them. Also, Canada. Most are in Europe.
Just read one book on them, reading another now.
Probably going to be what I do when I finally buy....
But if I end up renting for a few more years, may just bite the bullet and get a nice stove to move around (as I got a buddys to store wood at, he doesn't know it yet
).
What I like is the integrated ovens, sleeping areas, lower radiating temperatures and seemingly ease of use. Build hot fire, refill, refill, burn down, pull damper (could even automate a 'sniffer' for the damper). Also, since you are using hot fires, they make use of some of the less than desirable cuts for most people. The hardest thing would seem to be measuring out the wood loads, so you don't overfire and crack it. Corpicing trees, where possible, may actually provide better fuel and faster regrowth (apparently 'corpicing' or pollarding was very popular in the 'Little Ice Age', when they were most concerned about making the best use of their woodlands).
I think plenty of practice in masonry projects before tackling a masonry stove, would be advised from my readings. In Europe a stove mason may only build masonry stoves (thus accumulating a lifetime of stove building knowledge).
Not saying you couldn't do it, first time without masonry experience. But chances of making minor mistake that turns into a crack, may go up.
But they better be some turn-key plans and parts, because there is a lot of bricks to move should you not put in the right expansion joint develop a leaking crack. Or if you unknowingly use some cement and have to tear into it...You may be spending $$$ on new bricks.
It's not just about it being easy to get the bricks laid... It's did you do it well enough that you don't have to take it apart and rebuild it.
A lot of mass, a lot of heat = a lot to go wrong on the build.
But if they market the plans and materials together, or are very specific on materials...Could be done.
Supporting it is always the first problem. 2 to 12 tons is a lot of weight over a small footprint.
Then there is the plans... The stove can only be as good as the plans. There are differing schools of thought on the design. Which one is best seems to be personal preference... As long as the dimensions and materials are in order, so the masonry absorbs the proper heat before exit, the type of design shouldn't be too much of a concern.
But since some designs were developed over hundreds of years of trial and error... Might want to see if he's copying an existing established design, or being creative? If it is the latter, ask for his credentials in thermo-dynamics.
I'm planning on starting some foray into learning masonry to see if it is feasible to do it myself, or better off hire a qualified mason (w/ experience in builds).
Then there is also the issue 'response'. Many, many issues to address with the heating needs too. You have only so much of a heating range with them, so they need to be sized accordingly, for the house/room.
But instead of turning down airflow and increasing combustion temps or using cats, like the EPA. The N.European countries give the incentives for the building of masonry heaters. They have found them to be safe and efficient, and the numbers/test tend to back that claim up.