Hi there. Just wanted to clarify that the "email invitation9" functionality that we have on Tribe will send an invitation to every user that includes one link for registration that only works for the email address of that user.
If you are looking for a link that is shared and anyone can use to join the community, then the registration is not private. The registration is public and the users who received the link from you can share the link with others and the circle continues and you will have many users that you have not invited.
Having said that, if you want to keep your community private, you need to make sure that only invited users by you are able to join the community. Therefore, the invitation link should be used once only and should vary from one person to another.
FYI, later on, we add a feature called "Registration by approval" that alls users to request to join the community and you as an admin can either accept or decline it.