I've only used this for a few weeks but I feel like this add-on has changed the way I browse already. It's wonderful to save sessions for different purposes, like one session of looking at Emulation websites, one session for seeing sites about a certain game/show or another session for my work/email. No longer do I have to keep one of each around to switch to a different kind of browsing and have the associated memory usage. I can open my browser to a single new tab and use session manager to find the session I want to use. I give it 4 instead of 5 due to a IndexDB issue which thankfully solved itself upon browser reboot, it hasn't popped up again but it does pose a reliability issue for the add-on.

Highly recommended, should be a feature for stock browsers in the future IMO.