Yep, and "Sessions" is dead, too. I downgraded back to Safari 11, as I can't live without it.
But two thoughts on Omnikey:
1. It's from a hobbyist developer. If it's clunky, engage with him, encourage and test him to fix what's wrong. Don't just sit back and complain, it's not Excel.
2. Can't imagine how it works in Safari 12, as Apple has turned off manipulation of URL field from Safari extensions.