Like some others who have rated this add-on, I've been looking for a OneTab replacement. Tab Stash seems very promising in this regard because it offers much greater flexibility. When I first started using Tab Stash, all of the available options seemed confusing, but after using it for a while, I am now impressed.
One suggestion I might have for improvement, however, is to add the ability to select am existing "stash group" when clicking on the toolbar icon or the icon in the address bar, so tabs can be stashed directly instead of moving the tabs into a new group requiring me to move them later. I realize I can accomplish this from the sidebar, but it would be easier to do it my way.
It would also be nice to have an option on the options page to leave a tab alone after stashing it, rather than hiding or closing it.
Third, I'd prefer to have an option to not save deleted stash items at all (i.e., not even for one day).
Finally, being able to rename stashed items (not just groups) directly would be nice too instead of having to do it through bookmarks.
Still ... excellent work!