These balls are great for the price. I can't compare it to other branded ones I've used, but these feel good in quality and play great. Feel a bit sturdy/ and an average between light and heavy. I'm not sure what the difference is between the 3 star Optium (which this one is) and the 3 star competition which is about three times the price of this so I can't give an accurate feedback on them, apart from the fact I think they are good quality balls.
Decent table tennis balls. No seam and feel like they are the correct weight. We've been using these for many hours now over the last couple of months and they are still in going strong.
Make sure you buy 3 star balls if you want to have a proper game of table tennis - one star or no star balls are completely different and change the game completely. Playing table tennis with a no star ball is akin to playing football with some featherweight child's ball instead of a proper football.