Outside collaborators in a FREE plan organization

I’m trying to add an outside collaborator to my organization. The feature looks somehow buggy.

  • I access the Outside collaborators tab and if I send an invitation the invitation is filled as a organization (full) member.
  • Once this invite is accepted, the new member of the org can be moved as an outside collaborator. If I use this option, the member gets removed from the org.
    Also the UI looks strange, each tab has a different content width

(I only can put an image. This one is from the Pending collaborators tab, it takes only 2/3 of the full width)

Is this feature available for FREE organizations?