Additional features, settings, or issues not covered by specific Microsoft Teams categories
I was concerned with this but our external presenters worked great.
NOW, they did both have the Teams app and had used Teams before.
But I just added them to the live event setup as a presenter using their email addresses and when the time came, there they were.
We did test beforehand to make sure they were able to join and when we had no problems, we went ahead. You should test with a mock event/runthrough first but the functionality seems to work just fine.