[...] "It is claimed that the oil need only be added on every third fill so on its face that would seem to be a saving of about £1.80 over the three fills BUT surely the effect on the second tank is less than on the first and the effect on the third is reduced even further so the total saving might be £1.50 or less over three tankfulls a saving £1.50 or less on an expenditure of £270 hardly seems worth any effort." [...]