Waste of money, complete shit to be honest.
I read about it on this forum in a thread where someone said it has increased their mileage by 100+ in a tank, and gave this as proof
As i always buy the cheapest petrol, i thought id give it a go.
Ive ran two full tanks of it to make sure any leftover standard petrol was used. Its a 1.4 16v 5 door astra g. Driving style and routes have all been the same as normal. Full tank, petrol light flashing at around 365-370 miles. Exactly the same as when i use the cheaper petrol.
Conclusion - Waste of money, no performance gain and no economy gain. Stick with the cheapest supermarket petrol you can find unless you have an engine designed for higher octane fuels and/or is mapped for specific octane.