I would be careful with the “16A” rating on the Sonoff. That is what the relay inside is rated for a resistive load. Washing machines and other motor driven appliances have very large starting current requirements and they fire a transient spike if switched off while running. As long as the relay doesn’t trip when running or try to start when closed, you should be fine. Otherwise expect a very short lifespan on the relay in the switch.
You might want to look at the GE 14284 z-wave switch. It is rated to handle motors, is water resistant, and meets US standards. $33 on Amazon. Works with HomeAssistant.
Don’t know if they still make it but I had one of these that also had an energy monitor included so you could see the power consumption as well.
Personally I wouldn’t want the liability of a switch that doesn’t meet motor switching requirements.