Good point actually about the fuel cost, given unleaded is now around 5-6% cheaper than diesel, that cancels out some of the economy benefit..
Have found diesel MPG claims to be just as wild as petrol TBH, my TT TDi quattro never did much more than 45mpg, which to be fair isnt bad but it was a light car.. I did find on long trips it was handy for example driving from East Anglia to North Scotland you didnt need to fill up at overpriced motorway services !