So... the version of Outlook I have is compatible, but it looks like MSFT is being, well, very MSFT like.
My work email address is run through Google, and I use the Outlook 365 client to send/receive mail from a number of different accounts. Looks like the Add-in will only work if one connects a 365 e-mail account to it.
How stupid - as that will just push me away from Outlook. The Chrome extension seems to work fine. So away from Outlook and over to Chrome I will go for important sales related 1:1 e-mails 🙄