I didn't like them either (the IPong balls) but they were free so I can't complain too much and I appreciate very much all that the Joola guys have done when they visit our club. I especially enjoyed hitting with Steven). These IPong balls are like the XSF balls that I got to try almost a year ago (and the balls made in that factory more recently are a lot better). But mobilebeatz is correct that even the good XSF balls give up more spin after they hit the table than seamless, but that is I think because they are not sliding. Also I suspect they may be the largest of all of the polyballs in terms of diameter. On the other hand, I really find the very low bounce of most current Chinese seamless balls to be a very bad feature, and I hope the more recent ones get better (all the ones I have tried date from June).
For my money by far and away the best 40+ ball is the Nittaku Premium Japan version. It is a seamed ball and it is very different from the Nittaku SHA 40+ that is made in China. I got a few that arrived about a ten days ago, but they are again back ordered. Until I can get more I still prefer the XSF over, say, DHS. The good XSF are pretty round, very durable, and have better sound than the IPong balls (or most seamed polyballs).