The new one-to-many buddy system works by giving players a URL to share with friends that can be used repeatedly. Not only that, but if one friend isn't interested in using it, the URL can be forwarded to others who might. Then the player who put out the public invite gets the reward for anyone who uses it and subscribes, regardless of whether they know each other or not.
Direct personal invites will still be available for players to use, albeit without the PLEX-for-PLEX reward option. For more details, check out the official dev blog.