I am an OAP and the ever increasing cost of fuel is a concern to me. I have read various articles on ECU re-mapping devices, all of which claim to enhance fuel consumption and performance.

Some guarantee a minimum 20% improvement in fuel consumption. I run a Saab 9-3 Aero diesel 180 saloon which averages about 45mpg. My annual mileage is about 8K. A 20% improvement would mean 54mpg. Are these devices as good as they claim to be?

Also, as they also increase power output, how would this be regarded by my insurance company? I don't want to ask them directly, in case they assume that I am going ahead and load my premium!

Lastly, are there any downsides to engine safety and longevity if I fit one of these devices? I really would appreciate your advice.