it feels different. pack vs low speed dampening vs plushness. If all you ever needed to do was change oils, there would only be 1 set of pistons available. When ever you buy a used roller, you should always take the shocks apart. Check the pistons, the amount of limiters and replace the oil. You need to know your car inside and out, so you know where you are and get to where you want to be. I have had several guys at the track say my car is pushing or it feels unstable. Then, I ask, what is in your shocks. Several will say, "I dont know". At this point, I normally giggle, wish them luck and suggest they open up the shocks when they get home. I often buy lightly used kits because of the cash saving and the chance of getting tires that work at my track for cheapish. But, I tear it all the way down, check for stripped screws, rebuilt/set the diff, check out the shock package and look for worn parts in need of replacement. If it is a kit I have never owned before, this also lets me get a feel for how the car goes together and how to fix it. Plus it can highlight what tools I need for the car. i.e. the Kyosho shock tool is trash and best to replace.