Hi yes, you still need the gateway. You need only one gateway for multiple devices. The gateway connects to the MQTT broker providing control of all connected devices, and in its turn connects through radio to each device.
Device (Timer) <-radio-> Gateway <-MQTT-> MQTT Broker <-MQTT-> Hubitat
The gateway sends periodic status updates by publishing to the broker, or immediately when certain events occur. It also subscribes to the broker to receive commands from Hubitat, connecting to the end devices through radio to execute.
Using Rule Machine you can for example trigger watering based on a schedule or external events (such as readings from moisture sensors, rainfall data from a PWS or weather service, forecasted rain from a weather service, etc.). The driver also provides other functionalities such as alerts (e.g. if no water is running after opening the valve), wireless testing, water volume measurement, etc.
It is not cheap, but it is quite complete and has good support. Allowing local-only integration is a great feature that I am not aware of similar products offering. Of course, you also pay for the app and cloud integration, which with local integration you will not need, but I still think it is a good product.
