Warmed up with some new Micro X balls today ... my partner and I agreed they played like they were slightly heavier than a regular ball, but nothing that bothered us. We were hitting with new Penn ATP's at the same time for comparison. The Micro X's might have bounced slightly higher off the hard court (or maybe the ball has greater spin potential) but the difference was subtle.
From a static weight viewpoint, all these balls weigh the same. Out of the can, the Tretorns varied from 2.00 oz to 2.05 oz. The Penn ATP's varied from 2.00 oz to 2.10 oz.
I think that any player perceptions that the Tretorn's are slightly "heavier" or "harder" has to do with differences in the elasticity of the ball and differences in how they deform on impact. Would be interesting to watch a high-speed video to see if there are any visual differences.
My elbow can be a bit sensitive so only time will tell whether the bag I'm about to order will mess with my arm after some machine sessions.