Without a way to throttle the output of the heater a reset unit will not do you much good, and can actually damage equipment by excessive short cycling.

They can be very effective, however when applied to cast iron boilers their effectiveness is limited since they should be operated above 140 degree operating temps to control condensation on block. A oil fired boiler in condensing mode is especialy bad because the soot in the combustion/flue products makes a sticky paste that will plug a block quick.

In your case could be way more trouble than it's worth