If you look at big size heli, most of them use TT. TT is more friction free. On belt drive, when you rotate the main blade by hand, the blade will spin, say, 3 full rotation. But in TT, it can spin at least 5 full rotation.
If you ask Wayne, he prefer TT over belt. Am I right, Wayne?
But think has change, Goblim and some other brand use belt for their big size machine.
When you install the TT, finish the tail assembly first (tail shaft and housing). TT already in the boom. Slide the boom into the boom block, then back up a little (+/- 1mm). This is to get a good gear mesh and the TT is not bending inside the boom.