Any help in helping me understand this and decide what to use is much appreciated.
You need to spend the time and resources to upgrade. Syncrepl is unreliable in 2.2. N-Way MMR is not supported until 2.4. Until you can upgrade to a modern, robust, supported release, you're pretty well stuck, although certainly at least having a master/replica using slurpd is better than just a single server.
--Quanah -- Quanah Gibson-Mount Principal Software Engineer Zimbra, Inc -------------------- Zimbra :: the leader in open source messaging and collaboration