This set of lateral links completely changes your rear suspension from rubber-bushings to full spherical joints. The result is vastly sharper handling from the back suspension as the control arms can more accurately locate the wheels. Yes, there may be a trade-off in terms of increased vibration into the car, but we honestly didn't notice that, while we did notice the car tracking better into hard corners.
Set of four lateral links and two end links. FIts all '02+ WRX, including STi. (The STi already has this suspension design, but uses rubber bushings instead of spherical joints.)