I personally wouldn't bother fitting one as they are not cheap and totally fallible if the car is being attacked by professionals.
I do however know of a success story from 2 years ago when a mates Lotus Carlton got stolen. He saw it go, reported it and it was recovered 2 miles later in traffic with the crim inside. Steve walked up the road to recover his car and the tea leaf was sat in the back seat of the cop car.
Steve flicked him the bird and then got in his car and drove off.
