I don't think the Nyrod changes length very much, I think the airplane does. The coefficient of linear expansion is much higher for the balsa than it is for the plastic. So trim changes are because the airplane itself has expanded in the heat or contracted in the cold. If the Nyrod manufacture did improve their product, then they must have made it expand and contract more.

The easiest type of rod to install is the stock plastic rod. BUT, this is easily changed out later if you don't like it. So, you aren't locked in.

Many modellers will try to avoid using the Nyrod brand pushrod, if they can. Sometimes, nothing else will work. They do tend to introduce a tiny bit of "slop" to the control linkage that is noticable in precision aerobatics and higher performing models. For trainers, its not that big of a deal.

Those composite rods look very interesting !! I would like to try those. They might just be the best answer.