Bartender 3 (version 3.0.8 as of 1 October) is available as a free upgrade from version 2. The new Bartender menu is a stroke of genius – instead of expanding to show all menu bar items or to show the hidden ones below the menu bar, it now toggles between visible and hidden items. Version 3 even properly hides the AirServer icon, which version 2 could never do. A half star off because sometimes a few icons end up in the wrong spot.

This has only worked half-assed on Sierra.
And the dev. is another deadbeat who doesn't respond to messages.

WTF do they have a "contact us" page if they aren't going to respond?! Should call it a "DON'T contact us" page.
https://www.macbartender.com/contact-us/

After every reboot some icons move to the left side of the menu extras. And the eject button can no longer be hidden.

All requests to the dev. have gone unanswered.