my experience of it also.
TDi arosa.. zero difference.. if anything been slightly worse mpg since.
Leon Cupra TFSi, diddly squat difference
Its a fuel system cleaner at best, introduced @ the fuel rail so there onwards is its "cleaning path"
It might be burning off from higher temps some carbon, as some folks have reported benefits, but it seems not everything will benefit
There are other cleaning products which do decarbonise and are usually added thru the intake system so all the intake see's the cleaning