For now, I poll modbus addresses every 10 seconds (testing here).
My modbus devices are normally autonomous: I program them to run tasks, depending on rules and triggers (my plc has relays but also analog and digital inputs/outputs). PLC's are very reliable (industrial use: $$) and I trust them more than any hub. And I have a full network of ds18b20 wired temperature sensors: easier to put anywhere (including soil, water or deeply hidden into machines). And they have built-in smtp management (alarms, reports, etc).
The MQTT-Modbus link is made to harvest non-critical data (like temperatures, electric metering, liquids pressure and flow) and display them into HE. In certain cases (by example a specific task should be made manually), the link will avoid that I reach my plc for doing it.
To summarize my needs: Lazyness and willing to obtain a better interface (through HE)
Here are screen captures of summary made with my PLC (IE only - ActiveX)...
And today I received a new modbus battery monitor that will be hooked into HE... to display the status of my battery bank.
