I've used both, they both do basically the same thing. The Scotts is a hard anodized unit, I can't say for sure w/ this GPR setup I've got. I DO know GPR has excellent customer service...at most big events they will rebuild at the track for free.
Performance wise...I can't tell a difference, although the GPR seems to reduce arm pump even more than the Scotts-not sure why. They both are a must have in terms of damper vs. no damper. I do like the larger knob on the GPR...pretty nit-picky. Both good units. If the GPR lasts as long as my Scotts, I'll give the nod to GPR.
On some sites I have read that the Scotts does not have return damping but the GPR doe. Is this good or bad. Also, I was looking at damper combos and the scotts one is $80 more then the GPR. Is it worth the extra money to get the scotts with the high speed damping to. I race hare scrambles and was wondering which one would be better for it.