On Paper, Collections on Android are a very welcome feature, and make a good equivalent to bookmarks, tab groups, and various "Tab Stash" style extensions.
What's kept me from using them to their full potential however, is the simple fact that when adding mass tabs to a collection, they always remain open, forcing me to close them manually.
A simple toggle in the settings to control this behavior, and set the tabs to auto/close when adding to a collection, would be very nice.