Am super happy with this pin stopper.
It uses a very clever but very simple design for adjusting the length of the cord attaching the stopper to the chair. In this way you can fine tune the length with one hand even while holding the cello in the other hand.
However the multiple holes in this chock means that even if your first guess is only ball park accurate, you probably won't need to adjust it anyway because you can choose one of the other holes in the plank.
The only tiny criticism I have is that the back of stopper is wood and thus a bit slippery. So if you move around a lot the stopper might move a tiny bit. I ended up gluing a bit of antislip mat to the back of mine, but there's a good chance you mightn't even encounter this problem in the first place.