I've only just realised this is built into chrome natively:

Right click on any tab in a window and choose "Bookmark all tabs..." from the bottom of the menu. Or press CTRL+SHIFT+D.

This has the following advantages over OneTab:

1. You can add new bookmarks to the list at any time.

2. Bookmarks can be synced with google sync.

3. You can name the folder so you know what the list is.

4. Bookmarks are searchable in the omnibar.

5. You can open a single bookmark without it being removed from the list. If you don't want to keep it, just click the star in the address bar and then the remove link.

6. When right-clicking a folder there's an option to open all bookmarks in an incognito window.

I can't believe I've overlooked it for so long! I don't need any session management extensions now.