[Tannaton]

^^^ What he said.

Don't waste your money.

Some in-tank additives as an octane boost do have some benefit, but you might just as well buy the premium fuel (or use a 10% petrol mix every now and then, which I know is controversial but lots of people still do it...)

In tank cleaners are snake oil. If they were any good, they would dissolve the crud in the bottom of the tank and fuel filter and then drag that through the high pressure pump and injectors - not what you want.