I played with these G40+ at the MDTTC maryland National Training Center April Tourney recently.
I pretty much agree with Baal, and anyone would be plumb crazy to disagree with Baal on his opinions of plastic balls.
The balls make a very irritating ping sound on bounce. The do indeed feel more solid than their weight. They carry spin longer in air. They do not dip right away on heavy topspin at the table, but in off the table counterlooping, these will allow you to load up the spin as much as you can with a plastic ball. In such a loop to loop rally, the G40+ will seem to come at you FASTER, which requires an adjustment.
I adjusted within the time of 3 matches of my round robin group. The bounce on a passive short push or light spin ball that lands deep wasn't as unpredictable as the Joola ball, which ought to be melted with a welding torch.
I didn't break my bat or opponents'/Tourney Director's bones during the matches, so I guess that was a positive sign.