The hubserialixed-usb-hub-uart-for-pi-zero-w board has actually improved my x10 control via a cm19
even with my Zwave Dongle plugged in as well. That is not something I could say about using a plug in USB hub.
Using this with a Cm19 was just an experiment as I had plan to use it with a Cm15 eventually.
I doubt my Cm15 control will improve using this addon board but who knows