Okay. I think I have found out the answer to my question.I'm referring to a password program's ability to use some kind of system automation to fill any input field on a webpage or in a standalone application. I think that's what you mean by "keychain auto fill thing", although it has nothing to do with the keychain.
1Password can even fill in the authentication prompt on macOS when you have to provide administrator credentials.
Agile Bits does not want to support MacOS Autofill (Credential Provider API) at this time because it limits the company in features they offer. Additionally, it seems like the Accessibility approach is their "workaround"
I'm linking to two posts that seem to explain their position, and the disappointment of some customers - including me. I'm guessing there may be more posts on the subject, but I don't have more time to search right now.
One Here... and the other Here...
Now my question is whether or not to use the extension, accessibility "workaround" or Apple Keychain...
Decisions, decisions.