In the past, you have had a jet that pounds the same area of your body, "NO MORE"! Our new Whirl-Jet revolves on stainless steel bearings, enclosed in a plastic housing assuring constant movement with no drag or friction. The difference is the massaging action to your body and so invigorating that a standard jet will no longer be satisfying. Upgrade price is per jet,MUST buy jetted whirlpool system when specifying number of jets, then upgrade each jet.