There are several versions of Tretorn balls.
There is also a pressured ball with a treatment that helps keep the pressure good, a chemical lining, I think. It is the Serie ball, as used in Challenger matches. I found them very true, with a slightly lower bounce, and they keep the pressure well.
There is also the Comfort version of the pressure less ball. It is less 'hard' than the original X ball.
They do sound a little different when you hit them. IMHO a whole lot better than a flat dog tired Wilson etc. I really don't like the extra duty versions of some balls like Slazenger, and find them hard.
A tube of Head ATPs would last me about four hours indoors, spread over a max of two days, after that they are fit for the bin, so maybe I like a hard ball.
I think Uncle Toni made Nadal play with rubbish balls, strings etc to teach him that a winning attitude has nothing to do with perfect conditions.
So try out some of the Tretorns and don't go by other people's experience that is based solely on the very first Tretorns on the market.