Heat is heat. If the system is sufficiently exothermic to overcome losses, and sufficient heat is returned to the reactor from the cooling system (if there is one), the reactor will run without further electrical heater input. If the returned heat is excessive, thermal runaway will occur, absent a controlled, forced cooling system or some way to control the generated heat. Control of generated heat is not, as I recall, a convenient thing to do with Mizuno's reactors.
What I would like to see (and kick me if it's there somewhere) is a list of runs, for R20 at least, for each run, how long the runs were, how much input power was used and excess power produced, plotted against time and also the total energy for that run. I know that's a lot of time and work if there are a lot of runs.