No they won't. Controllers are for that very purpose, reducing erratic temperature swings.
Contrary to what most people think, controllers (good ones) don't just switch the heater on when the water temperature reaches a set minimum value, or off when it hits a set max value.
They look at how fast the temperature is changing, the accumulated error (difference between your set point and the actual water temperature) over time, as well as the current water temperature, to determine when to turn on and off the heater.
Layton