Thanks Dartman - I guess you're talking mpg whilst towing? Did you see much improvement when not towing?Sorry about that, I was experimenting switching between Low and High torque settings, I got about 26mpg, but unfortunately I had head winds both ways, I remember getting 28mpg on one of the fills, that was brim to brim calculated, not indicated. I think they are worth it just for the torque you get when towing especially when you get a Micra or similar doing about 40mph you definitely have the power to get by quickly, which then allows you to roll along in top economically. I think I don't get the much improved mpg because I use the torque in the gears to progress the journey, in other words I use it to overtake when without the box I couldn't overtake at all. Best setting for economy is Lo torque and Lo bhp. Use Hi torque and Lo bhp for hilly areas and strong head winds.