The one downside of direct add is visible in your comment:
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¡°I don't like invitations because the recipient has to recognize that it's a legitimate invitation.? Receiving an email from <groupname>@groups.io may not catch their eye, requiring more work from me to follow up. ¡°
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Since that¡¯s what the list will show up as, if they don¡¯t expect it, they mark it as spam and get bounced out. At least the invitation helps them to know what this sender address is doing.
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All around there is no perfect solution. But careful use of the tools are our only shot to get it done.