Regarding the bit.ly documentation it was a bit of a struggle to get the appropriate OAuth token generated. Bit.ly service can also use OAuth Webflow token. This addon requires the simpler OAuth token and it has to be used in the extension's Custom URL pulldown option rather than Bit.ly option.

I was using a now deprecated URL shortener which had an option that would also capture the Title of the page and insert that into the clipboard. I found this useful when pasting the information into email or on Twitter. This way one could see what the URL is for and saves having to type that information in.