Does what it says. There is however room for improvement. My suggestions:

A toggle which sets whether or not put aside bookmarks get closed. Sometimes you might want to save different sets of tabs with one or more of the same tab in each.

A second toggle on whether or not set aside bookmarks are deleted from the bookmarks when restored.

The ability to set the root location of the set aside bookmark folder. This would point to the folder above it to use (currently "Other Bookmarks"). One advantage of that is that you could point this is a folder on the Bookmarks toolbar.

Maybe the ability to rename the the sub-folder the set aside folders are saved to. Currently this is the name of the active tab. Maybe what would happen is that (like the old Tab Mix Plus) you'd get a popup with a text field defaulting to that, which you could edit, before saving or cancelling.

Just some ideas. Keep up the good work.