Has the potential to be(come) great, but for now not useful - for me.

You cannot drag closed tabs to different window.
You cannot drag windows to a different session.
Sessions can't be organized in folders.

Tags for sessions are useful, as you can filter them. This is nice.
Auto-track change option is also a good idea, but it has to be activated for each session individually - it seems.

For now it seems a good extension for people who want session syncing for sessions containing multiple windows.
People who want to sync WINDOWS (1 window = 1 subject) will find this extension less useful.