The AWR 21.5mm rear swaybar makes a huge difference if you're planning on tracking the car. It will definitely take care of the understeer. It will also lift a rear wheel every time you go up a driveway at an angle, clunk endlessly, and burn through swaybar brackets about once a year.
I ran an AWR bar for years. NVH (noise, vibration harshness) is always a trade off with performance parts, especially suspension. The swaybar will make the car corner better, but there will be some ill effects too.