Ultimately this is an architectural decision and it will be dependent on your unique circumstances. Arguments could be made for connecting to either Kafka or the MQTT broker. It is possible to expose the MQTT broker outside of the Kafka cluster if this needs to be done, but like you mention Kafka is there for a reason — compensating for deficiencies found from the experience of trying to use the MQTT broker alone. As you weigh your decision, consider whether it makes sense to have multiple instances of the UMH in your environment (at the area or site levels perhaps), what services are connecting at the edge versus what services run & connect at the Enterprise level, the need for reliability, etc.