I have often wondered about the potential fuel consumption benefits of a K&N filter, the performance differences would be too difficult to quantify anyway. Being a fairly steady, routine routes and trips sort of driver I decided to try on on my 2018 Jazz Sport. I was going to base the trial over 6 fills and compare to the previous 25 since new. Now having done 3 1/2 fills (1265 miles) the results look like - 0.8mpg/0.18mpl improvement, i.e 7.04 miles range increase in full tank. This is a 1.69% improvement in range, and with my sort of driving style and use would require another 23 full fills at today's price locally (£1.239/l) to get the filter cost back - though a cleaning cost in the future will have to be included. I will update when 6 fills carried out. Performance - I do "feel" the car is more responsive in acceleration, this should be treated as tenuous at least. Hopefully will help others who may be thinking of this sort of refinement.