I have an older model Keystoker (about 10 years old). I find the stove to be VERY well built and very efficient. Using a Honeywell "The Round" thermostat, it will hold within a few degrees. Only issue with my stove's design is that it is very difficult to clean the upper reaches of the heat exchanger. But, the stove is fully double wall construction, so the outside of it never gets above hand warm. My exhaust gas temps hardly make it into the triple digits!
The newer Keystokers have a totally different body design, and the sides of the stove get HOT! I don't think they are as efficient, but much easier to keep clean.
The stoker mechanism itself is the same, and VERY well made. They are good stoves, and the factory is very pleasant to deal with and prompt.