Optional
When I started building in the early 90's rudder springs were often mentioned as an option. I even made provisions for them with my cable to pedal connector plates but never installed the springs. No issue at all without. The only time you need rudder on a 6 is when you are taking off or landing, then you will have your feet on the rudders 100% of the time and will not need the springs to take up slack. Once in cruise you don't even use the rudder pedals. I usually continue to rest my feet on the pedals but occasionally will want to change position and pull my feet back and off the pedals, no affect on flight characteristics at all. IMHO springs are not needed.