No a rheostat is like a dimmer on a light bulb. A controller works as a thermostat where you can set the temp and it will turn the heat on and off to keep the area at that temperature. Reptile supply is where I purchased a Zilla (formerly ESU) controller.
They have two from Zilla one will handle 500 watts and the second handles up to 1000 watts. Here is the link to the 500 Watt model.