Hmm, their BE still does a bit as it facilitates the connection of two devices with another. The clients are independently connected to it and if two want to talk with another, they first talk to the BE to coordinate the firewall piercing on both ends.
Still, given that an OSS re-implementation exists and is in no danger of being canned (TS went ahead and hired the person who made it lol), it being proprietary isn’t a big deal.