Rated 4 out of 5 stars
I have found this addon to be a new essential. It does everything I want in a sidebar and nothing more. No huge chunks taken out of my screen estate. It is small and relatively unobtrusive. Overall, I'm extremely happy with it.
I did find a small issue with Tree Style Tabs. The tab sidebar size will drastically reduce until I 'customize' the toolbar (which temporarily places the tabs under the navigation toolbar) and click 'Done'. This makes everything look perfect. It is not a deal breaker for me, but it can be for less computer literate people (non-programmers). Noteworthy, this behavior is not reproduced with the Vertical Tabs addon.