Let's think about this. I usually get about 28mpg fill up to fill up. But the variation is between 27 and 31 depending on how many longer journeys I take. And the season. And 2% of 28 is about half an mpg. In other words, in normal driving (for me at least) any saving would be well within normal variation and so would be undetectable.
^ That has been running through my mind for some time. How do you really check it does what it says on the tin. At the moment Shell is a penny cheaper per ltr than my local Esso garage. Both garages are on my daily route so I shop at Shell.
People saying "If it is no more expensive that the normal stuff" Keep up this is now the normal stuff at Shell stations. Other options are V Power or V Power. I almost exclusivly use Shell as the forecourt is about 500 yards away. Will I cut more grass trim more hedge and strim more edges for my £1.00 I hope not I hate gardening.