They're rock hard and very hard on the elbow and a little oversized a la the Dunlop Grand Prix balls when you first get them, they bounce like super balls at first, ridiculously high, almost over the fence high. I played with several open and all state players years ago using these and they were disgusted with them. They refused to play with them in fact.
However, once they got broke in a little after about two weeks of play, they're bounce subdued just enough to more like a regular ball (i.e. without the fear of the balls bouncing over the fence on heavy topspin shots...VERY annoying).
Also, after the initial break in period, they stopped feeling quite as hard and jarring on the elbow...which was IMMEDIATELY noticeable by the several players including myself who tried them out initially.
I think once you break them in, they're a great ball machine ball or hopper ball, but because they're really expensive when you lose them or a side court swipes them...it hurts just a little inside, feels like one more kitten in this world has been needlessly lost to neglect, so sad.
One thing to note, is that I've read that those who buy by the bucket will get balls that are less bouncy and lively than the ones who by the individually boxed 4 ball set as they are taken out at different times of the curing process or something was the explanation, i.e. the bucket balls are the left overs or something and thus aren't as lively...which I actually think is a GOOD thing.
I bought the 4 ball sets, so this may explain why they were unnaturally lively and hard. I remember one teaching pro on these boards called them rock hard, 'super balls' describing the way the old Tretorns he used bounced and played.
With that said, there IS in my opinion a better and MUCH cheaper alternative to the Tretorn ball out on the market now. Unique Sports sells them. These pressureless balls feel just like normal Penn Championship balls, are not slightly oversized like the Micro X or Dunlop Grand Prix balls, their felt life is adequate, and most importantly they do NOT feel rock hard and are not hard on the elbow and they DO bounce just like normal pressurized balls. I've tested them side by side with fresh Dunlop Grand Prix balls and they bounce almost exactly the same. I used to use them regularly when hitting with a former pro and a pair of 5.5 players. Had I not told them they were pressurized balls they would NOT have known and did not suspect anything. When they found out they were pressureless and so cheap, their only response was where do I get them?
These ARE the balls to get for practice use and ball hopper and ball machine use without a doubt. Maybe the Tretorns last a little longer, but then again Tretorns are harder on the arm and are priced at a premium. The Unique pressureless balls cost about the same as any ordinary grade championship pressurized ball, and thus losing a few to a neiborhing court of bandannaed pirates and thieves does not make you feel like going on bambi road rage if you know what I mean.
