Mazda 3 start/stop savings

I read Ray Swann's letter about the stop-start function in his Golf. I have a Mazda 3 which is fitted with i-Stop and I find it quite painless. It is controlled by pressure on the brake pedal. On normal stopping the engine keeps running. But if you think that there could be a longish delay then simply push harder on the brake pedal and the engine stops. Most importantly, the car has sensors to detect if cabin comfort is changing and will override the start-stop to start the aircon up again. On Sydney's congested roads it is a nice feeling sitting at a red signal in silence knowing that your car is emitting nothing. I have travelled about 20,000km and the computer tells me I've saved about 300km-worth of fuel in that time.