I have not had occasion to try mine yet. I have always had it on BMWs as well - hoping it is just as useful on the 911. There's not a huge difference in the price of the wheel with or without is there? I just replaced my wheel with an MF wheel - took about 2 months to get it though with heat - special order from Germany.
Indications according to the manual:
Switching on steering wheel heating
>
Press button.
The message “Steering wheel heating ON”
is displayed on the on-board computer for
2 seconds.
Switching off steering wheel heating
>
Press button.
The message “Steering wheel heating OFF”
is displayed on the on-board computer for
2 seconds.