That V-Zine also had an eco test: London to Monaco on one tank of diesel with three modern 1.6 cars. The Passat Bluemotion 'won' by a fair margin by the way, making 84.1mpg! (And not making the wait for my Ecomotive 1.6cr SE any easier...)
Slightly more on topic, from memory, they didn't specify if they brimmed the tanks with V-Power Diesel or their standard fuel, which I thought was odd if they thought the V-Power would give more mpg as well as the claimed engine cleaning abilities. One might conclude that V-Power diesel has more detergents but little performance benefit?
Yeah I agree, I think the properties of v-power diesel are to keep the engine internals cleaner for longer, thus like new!