Personally I'd use a proportional thermostat like a Herpstat or Helix. You set the temperature you want place the probe and done. No fuss, NO mistakes. My ball often pushes the substrate around and if it gets thicker or thinner the temps go wrong. Dimmers are ok but don't account for variable room temps if the temps increase in the room the dimmer needs to be shifted. I personally have quite a variation this time of year as the weather gets colder and warmer and the heat is low or off.