We’ve just released an improved version of OS 3 (the minor revision number is 3.2) that can optionally come with an Ethernet module. It’s already available on the product page: https://opensprinkler.com/product/opensprinkler/
You can add wired Ethernet module to the controller.
I am just providing an option for using previous OS 3.0s with a wired cable connection to your router. I am not sure which choice is better: the new OS 3.2 with Ethernet module reduces a layer of indirection (no pocket wifi router involved), but on the other hand it’s only released like a couple weeks ago and has not been tested over a long time so we don’t know if there is any software or hardware issues that may come up.