I can see why it makes a big difference, it allows the car to rotate slightly during proper cornering on a track, allowing the tires to maintain a better slip angle, one which allows them to be far closer to their optimal traction. Also by transferring balance back to the rear, the front tires are not overwhelmed as easily which gives them far more traction under hard driving. In addition to this, the rear bar provides more roll stiffness without contributing to problems associated with a car that has too much spring stiffness.
I have had the bar for a while, and as long as the car is driven properly (as i would on a track) the tail will not wag.
