Sadly, currently broken.
It guzzles memory and CPU time like nothing else I've ever used and really slows down the browsing experience. This addon should *not* be going to 80% CPU usage and adding 2-4GB of RAM usage just because I opened a single tab.

I hope it gets fixed soon.

edit: My mistake. The real cause of the problem was one of the settings in the Tab Session Manager.
5/5 for Tree Style Tab itself.