I always assumed Zertz was pure marketing hype. This spring I rode a Specialized Tarmac and Roubaix back-to-back at the dealer. Wasn't I surprised when I could indeed tell the difference! The Roubaix (w/Zertz) was noticeably smoother at the high vibration end of the scale. It had NO effect on bumps...we're just talking road vibration.

However, while the difference was noticeable it was minimal. I certainly wouldn't pay extra for it but it did make a slight but noticeable difference.