I really like glaera for low volume clustering, because of the true multi-master nature. I've been using it for over a decade on a clustered mail server for storing account information, and more recently I've pumped the log information in there so each user can see their related log messages, for a user base of around 6,000 users, and it's been a real workhorse.

Uh, that scale doesn't even need clustering beyond high availability.

And as Jepsen showed, if you actually do increase volume, it loses consistency... Invalidating the use case for multi master entirely. So, ymmv I guess