Back when I was working in a project for characterization of so called “biochar” made out of several locally available materials, we used a similar oven to make the Biochar in a very air restricted atmosphere to cause the pyrolysis. We set the oven to 250 +-3 degrees and It stayed there spending energy until you put a sample inside or turned it off.
Some materials produced a great heat during the pyrolysis (and many volatiles that ended clogging the oven’s exhaust) and at those instances the oven switched off all heaters and started a fan to cool down the chamber, so we learnt quickly we had to restrict the amount of material put into the oven in each batch to avoid the samples to burn entirely by overwhelming the capacity of temperature control of the oven.
This is just an anecdote to illustrate that I have used these kind of ovens and if I had to use it for testing a Mizuno reactor a would go The way already described, by measuring the heat input compared to a control / inactive reactor.