That video has been used for a while now to show how great the low balls are. The balls are easy to play with and the kids can have fun with them.
The problem we see is that many kids get fooled and do not realize that tennis is a running game. They get destroyed when they switch to yellow in many cases.
We have kids who play yellow and go 'down' to the green or orange level to compete sometimes. In a week they can easily adjust and win vs the slow ball only kids. But the slow ball kids get slaughtered when they try to move to yellow.
Tennis at the junior level is hard. Its hot, the yellow ball kids move you, they hit high deep topspin. You have to move like a demon to get to balls, you have to have great footwork and be able to cover the court for long rallies.
Many of the low compression ball trained kids are shocked to find out how much they have to move on a full court.
The mini tennis video is cute, but there is no way to know if those kids would bust it on a full court anymore than knowing if a good ping pong player would.