Tree style tabs used to get very laggy when you have lots of tabs open. Sideberry performed much faster. So I switched to it.
Interesting. How is it better?
For me, I really liked how it has "panel" functionality that also let me replace Simple Tab Groups, and how nicely that interacts with Multi-Account Containers. I have a panel for work, and when I'm done with work I can switch to another panel for another task and no longer have to look at my work tabs - then the next day I can have just those in my tab bar again.
Also an user of Sideberry, from my experience it just works a little bit better than TST.