I too used to use Regane but after trying SI-1 I'm not going back.
Red Line is more expensive but you get 2.5x volume and higher concentration, and it did smooth out engine and gave me much better gas mileage almost instantly, well within about 60 miles of driving.
The way I look at it - it cleans gas tank to some degree by dissolving gum, cleans fuel pump in tank and high pressure one on engine, fuel lines, injectors and even combustion chamber and top of pistons, all while improving gas mileage. The must be long term benefits to this like extending above mentioned components life.
Red Line is more expensive but you get 2.5x volume and higher concentration, and it did smooth out engine and gave me much better gas mileage almost instantly, well within about 60 miles of driving.
The way I look at it - it cleans gas tank to some degree by dissolving gum, cleans fuel pump in tank and high pressure one on engine, fuel lines, injectors and even combustion chamber and top of pistons, all while improving gas mileage. The must be long term benefits to this like extending above mentioned components life.