I knew before I bought it what I was in for fuel wise.
For day to day use I never go near a Motorway or anything resembling an A road, so it is all town driving, allbeit traffic free. Normal driving with the odd blip here and there and I get around 22mpg. If I'm extra carefull I can see 25mpg. When hooning I'm happy if I see 13/14mpg.
Done a couple of decent motorway trips, 40 or so miles each way. Cruise set at 70 it will do 30mpg all day long. On one stint I set it at 60 and it indicated 35mpg.
Those are all trip indicated, cba to work it out myself.
If you are worried about fuel I would stay away from one, but if it isn't too much of a concern then I can hand on heart say that 20mpg is worth it for the noise alone!