Finally a really good alternative to my old tab groups. It's optically pleasing and I didn't discover major flaws yet.
One minor error though: When using the Amazon fav icon as a group icon (right click on tab > set icon for group) it does show up on the usual STG icon but not when I click that icon to show the group overview. There it will show a not-found-icon. So far I could only reproduce this with Amazon (GER).