I have a Johnson Controls digital controller which I use with a thermowell.
I set the diff to 1 degree and the auto cycle to max.
This works great once the initial temperature has been established, but doesn't work if the initial temperature is more than about 3 degrees more than the set temperature.
When the temperature of the wort is more than about 3 degrees, above the preset temperature, the controller switches the freezer on and will not switch it off until the wort temperature reaches the preset temperature, by which time the ambient temperature in the freezer has dropped to about 20 degrees below the preset temperature.
I get around this problem by positioning the probe so that the bottom of the probe is aligned with the top of the wort. This prevents the temperature overshoot, and after about 12 hours I push the probe to the bottom of the thermowell which keeps the fermentation temperature within 1 degree of the preset.