Thank you for reaching out to the Zoom Developer Forum. Great question! The allow_multiple_devices property will prevent registered users from joining again but it won’t require that the users that registered for your meeting have a Zoom account or are logged into Zoom.
It won’t let the same email be reused to join the meeting from another device.
Thank you for providing additional information. My understanding is that the setting prevents users from joining from the desktop client and a phone at the same time. I don’t think it restricts the join_url from being used from multiple computers.
If you would like this feature to be considered for a future release, I recommend posting in the #feature-requests category.