I had my EOS tuned for the APR-93 Octane and absolutely love it. The performance increase is VERY noticeable with peak horsepower at 252 Hp, and torque at 303 Lb-Ft! Also, since the engine is tuned to run much more efficiently, my gas mileage has actually gone up by nearly 5 mpg (assuming I am not pushing the vehicle)! If there is a downside, it is in the "off-the-line" performance. The power boost turns the tires over very easily and if you are really pushing the vehicle from the line you must turn off traction control. Otherwise the car lunges as traction control attempts to take over with alternate braking of each wheel. I had the dual programs installed such that, through the use of the cruise buttons, I can toggle between stock program and performance program. This option is important if 93-octane is not available or if taking the car to the dealer for service. With the car toggled to stock program, APR is undetectable by technicians.
Also, with the exception of additional power, there is absolutely no difference in ride quality, engine idling, and engine smoothness between stock and performance programs.
Since I was already using 93-octane, I estimate that the gas savings will pay for the APR tuning in less than 2-years. That's assuming I don't push the car more than I would have...yeah, right!!!