I have been running a Synapse instance for nearly 3 years now. My instance is not for open registration but just for family and friends, currently it has around 7 users on it and federates with the rest of the Matrix ecosystem. I also have some experience writing apps that use the Matrix APIs.
The federation API on matrix is a little too chatty for my taste. But that in itself causes no problems. The problems start when a user on your homeserver joins a massive room on any other homeserver. Most commonly these are the bug rooms on matrix.org. Once someone joins one such room, synapse will start slowing down and taking tons of RAM. This has significantly improved in the last year, by huge leaps and bounds. It however does remain a memory hungry process.
VoIP / video on the other hand has been a success story for me. 1:1 calls run smoothly after installing a TURN server. Me and my users use the calling functionality multiple tines a day and don't seem to have any problems with it.
The federation API on matrix is a little too chatty for my taste. But that in itself causes no problems. The problems start when a user on your homeserver joins a massive room on any other homeserver. Most commonly these are the bug rooms on matrix.org. Once someone joins one such room, synapse will start slowing down and taking tons of RAM. This has significantly improved in the last year, by huge leaps and bounds. It however does remain a memory hungry process.
VoIP / video on the other hand has been a success story for me. 1:1 calls run smoothly after installing a TURN server. Me and my users use the calling functionality multiple tines a day and don't seem to have any problems with it.