I had them on my Mk5 golf and found it quite usefull, it rarely went off and when it did it was because I had a slow puncture. I wouldn't have known about this until it became visibly obvious. The system reacted to a 3psi drop which you can't see, I guess the Audi system is the same one which uses the ABS wheel speed sensors to detect a rpm increase in the deflating (and hence smaller diameter) tyre.