It is a slight buff for MM and SV hunters. Depending on the comp BM hunter is playing in, it's either a buff or a nerf.
40 focus cost is still unbelievably stupid to use outside of BW. I actually got to use tranquilizing shot once in pvp since its massive nerf to 50 focus cost and since hunters are most resouce-starved class in the game, the 40 focus cost will not change much on that. I will probably never use the glyph (I play MM and SV) and use tranquilizing now and then in hopes I dispel something else than a trash buff, or help my healer to dispel faster.
This change just adds more rng. Two independent stacks of tranquilizing shot on 10 or 15 seconds would be much better and more balanced around all hunter specs.