I recently converted a cheap consumer toaster oven and a hot-plate to PID controllers- I wouldn't expect their thermostats to work at all. In both of them, the adjustable bimetalic switch that controls temperature either at the surface of hot plate or inside the oven... is located right next to the switch itself- quite far removed from the temperature it is supposed to control.

It also means that the actuation temperature varies with room temperature and airflow in the room.