Sorry, it’s Wi-Fi only. If you have Wi-Fi coverage at the controller location, don’t be concerned about the additional traffic; it’s only about 60 kilobytes per hour. Also, don’t worry about reliability, the controller does a good job of automatically reconnecting after a loss of connectivity.
If there is presently no Wi-Fi coverage and you don’t need it there for anything else, a cheap repeater at less than $20 is likely sufficient.
If the Ethernet cable you mentioned is already present, consider adding an access point that will provide good general Wi-Fi for barbecues or other activities near the controller, or for other IoT devices such as fountain lighting or security sensors.