Obviously the added sand slows down USO, so you really can't compare it to USO. But in the Fed Cup final the court really didn't look that fast, watch from youtube. But tomorrow will show how fast it's for men.
actually I read that the USO is ranked at 5 in the ITF category, that is faster than this one (ranked at 4). Maybe adding sand can make the US Open surface slower than its classification, I don't know.
Anyway, as rocketassist said, Spaniards also complained a lot about the court in the USA which was only middle-fast, then I don't believe their whinings at all on that. But I just observe that they have managed to avoid really fast courts since they lost in France in 2010 (and I don't even speak of really fast courts as there were in the past in Davis cup
). Then so far I say "well done" to them. As for this match we will see tomorrow.