It will be cooler... how much, I don't know.
I used the thermoswitch location on the back of the waterpump using a NPT adapter for my gauge.
It isn't the ECU temp sensor. Mine is s5 turbo, so I don't know if your specific model has it or not.
FYI it is a one pin sensor and goes to ground at 207*, which you might find suitable (normal operating temp is 185-195ish)
