The main advantage of using the script-based plug-in comes from reducing the barriers to implementing new replication mechanisms. Rather than spending time learning about the Java, JMX, MBeans, or common agent container technologies, you can focus on the critical logic needed, for example, to set up a replicated configuration or change the direction of the replication flow.
The disadvantage of this approach stems from the very generic nature of the plug-in that makes it so easy to use. Generic plug-ins lack some of the tight integration that a custom module can offer. For example, the arguments that you supply on the command line to a script-based plug-in configuration are at the script argument level rather than the highly specific replication variable level. So, whereas the Geographic Edition Oracle Data Guard module has separate, specific arguments for properties like standby_type and replication_mode, an equivalent script-based plug-in version would pass these properties and their value as part of a single, anonymous bundle to a script. The script would need to determine the arguments and whether each argument is valid.