Hi Stefanut,

They’re OK, but we don’t think they’re the magic panacea that their makers (for obvious reasons) try to make out they are. They won’t improve your fuel economy by enough to offset the price of using them, so it’s really only to make your car a bit smoother running that you’d buy them. You’d be better off simply running the vehicle on higher-grade petrol and diesel in the first place, though, which features its own additives to keep engines and their fuelling systems in tip-top condition.