Apple - Is there a menu bar tool which will let me eject external drives easily?

Try Semulov - it is designed to eject volumes from the menu bar. The author has even made the source available on GitHub.

macOS included a built in menu bar item to eject removable drives. LifeWire has done a much better job than I could do providing instructions on how to add this to your Mac's menu bar.

Check it out here: Add a Menu Bar Item to Eject a CD or DVD

Update: This answer is incorrect. While macOS includes an eject menu, it can only eject optical discs.

Try Mountain. http://appgineers.de/mountain/ Not only does it allow you to mount and eject drives, you can select to not mount a drive on restart. I unmount a drive after cloning and don't want it mounted again on restart. This app does exactly what I want.