I found the Vyper chairs to be of superior quality and the backrest rubber a necessity. I even recommended to Vyper customer service that the backrest rubber be included as a standard feature of their chairs, and not a $13 (ok $12.99) option or add on. You can not go wrong purchasing the Vyper product, and the backrest rubber is a must have feature. I plan to purchase a half dozen chairs with backrest rubber to support bourbon tasting events at our home for our whiskey society...and a shorter version for detailing and working on my car.
This little rubber piece is a great add on especially if you are working around cars. Protects the back rest from rubbing and damaging anything.