Tried Super Gasoline Additive, Super Engine Oil Additive and Octane Charger.
I didn't calculate the change the fuel efficiency in details, but rather, would like to share my impression on the changes that they made.
Super Engine Oil Additive- Really made the oil last longer on my IS. Vibrations were not noticeable even after 4 months/>5k km. Fuel consumption remains stable. I reckon that rather changing oil every 4 months, can add this and extend the life of the oil to 6 months max for foot car.
Octane Charger- The engine becomes more responsive when flooring on the throttle. But at the same time, seems like the fuel goes fast. Not much difference on normal driving.
Super Gasoline Additive- similar to the Oberon. But really need more time and detailed recording to find the difference between the 2.