You can do a configuration push from one independent appliance to another if you don't want them to be part of a traditional cluster setup. This is done under System - System Administration - Configuration Push. You can set the first appliance to push automatically to the second both on a schedule and whenever you apply changes to the first.
Thanks, you're totally right. Silly me I forgot this option because there has been a lot of time I haven't used it. I usually create clusters and so the cluster service already pushes config to the failover