I demoed the 99s with fresh 4G and did not notice much more spin than usual except for my backhand slice which had more bite and backspin. My friend who also demoed it didn't notice any more spin in my shots. My forehand already has lots of topspin while his is flatter. He said he felt more spin with it and I noticed a bit more on his shots. After an hour and a half of us hitting with it, the strings snapped and were badly notched.
I highly doubt any Pro will play with the 99s but I can see benefits for the average player.
I highly doubt any Pro will play with the 99s but I can see benefits for the average player.