I just installed a Scotts damper on my 220 about a month ago and have 3 or 4 rides with it. My buddy swore they were essential and had one on each of his bikes, but I just couldn't see spending that kind of money. So he gave me one of his........what are friends for, eh? Anyway, it DOES make a difference, not only in rocks, but also in whoops, where the bike tracks straighter. I also believe it helps in sweeping turns. The bike seems to 'carve' the turn. I still don't know if I would pay $500 for one, though. Since I don't race, I would just get used to going a little slower.
By the way, I still had to buy the mounting kit, which cost $139, and I learned after the fact that Scott's only makes a mounting kit for a KDX with the handlbars in the rear position. When you order it online, it looks like you have a choice of forward mount or rear, but only the rear will arrive. However, when I went to install it, it didn't really fit in either position without bending the tower bracket, so I bent it so that I could use the forward handlebar mount. It is not quite the way Scotts wants you to do it, but it seems to work OK and does not bind.