Still the best of the celluloid balls. Rarely if ever see a bad one. Very consistent bounce until they give up the ghost. Yes they get dirty quite quickly, but it doesn't seem to affect the play. They make a truly wonderful sound off the bat when you catch them right, and seem to be able to...
I have this on a K7 - a nice hard blade and perfectly suited to the rubber as someone else said. It works (for me) just as well on forehand and backhand. Hard-hit shot and loops travel very fast indeed, on the other hand when you get into a pushing competition with some boring defensive merchant...