Excellent extension!
This one is useful not only for copying, but also to keep track of the number of open tabs. This avoids the need to install another extension for that, which saves memory.
Other extensions that I've tried also allowed me to count the number of tabs, but only showed the number of tabs when I clicked on copying, which overwrites my clipboard.
And as a bonus it can also paste tabs and copy all tabs using the markdown format.

I don't understand why the add-on requires to read from the clipboard. Can you explain all the permissions?