My refectrix cozy is round (fits my pot) instead of flat, so it is very efficient on holding the heat for freezer bag cooking. Like Fiddleback, my food is still too hot to eat after 20-30 minutes, so 212 degree water is not needed for the food, just leave the food with the almost boiling water in the bag for a few more minutes i.e. 15 minutes instead of 10.

Just pass your hand over the stove to check for the invisible flame. As you gain familiarity, cooking with the stove gets easier. I like not having to watch it, since I'm not cooking in the pot. Heating only water is so much cleaner for Arizona trips where the water is sparse.