Great, always expect great quality balls when it comes to Donic products. Very hard, durable and plays well. When testing, a slight wobble during the spin and it doesn't bounce as high as the balls from Butterfly. However, overall, impressed!
I've played some hours lately with this ball and for me it is very hard and also heavier than celluloid balls. Most of the balls in the package are round but there are also some which aren't round at all. It doesn't brake so quick as others.
I must also say I'm a bit disappointed with the quality, like benlarcombe wrote they breaks really easy. Some of them are round but sadly not close to everyone. This is the ball my club trains with, haven't tried that many new balls yet, but will try to make a review of all the balls I try in the future.
These balls are identical to the DHS and Double Fish plastic balls. They tend to split along the seam very very easily. Durability is terrible. They also feel pretty soft. I personally prefer the seamless balls and haven't tried the Nittaku Premium balls but I hear they are the best.