This is really just an additional feature of each of these modules. In most use cases, one would have MQTT Engine installed alongside MQTT Distributor in a ‘Central Ignition Gateway’. Then there would be multiple ‘Edge Systems’ that each had MQTT Transmission installed. The systems with MQTT Transmission installed would generally also be communicating with PLCs or other sensor/actuator data and making it available to the Central Gateway via MQTT.
Note in all of the above tutorial there is no scripting involved. All of the MQTT communication is done via configuration of the modules instead of scripting.
Since both modules are capable of publishing data via MQTT, they both contain a scripting feature to be able to publish data to the MQTT Server. But, for both modules this is not their core function.