I have seen success with it for many years. You can take the front and rear panel off and drop some of them inside as well. I have also used bobcat urine crystals. They smell it and think a predator is there and they tend to stay away. I have seen the mice chew thru wire mesh. Seems they can chew thru anything but steel. Mice love these heaters.
Also, a good part of my repair work is the visual inspection of units. When I come up to these units I always open it all the way up and remove the top to inspect. And yes even though mice may not chew wires, their urine will corrode lots of things. It is funny that they seem to know which wires to chew thru to prevent the unit from running. I see lots of the thermistor and ignitor wires chewed.
Also, a good part of my repair work is the visual inspection of units. When I come up to these units I always open it all the way up and remove the top to inspect. And yes even though mice may not chew wires, their urine will corrode lots of things. It is funny that they seem to know which wires to chew thru to prevent the unit from running. I see lots of the thermistor and ignitor wires chewed.