Can you just switch the mains supply on/off to the PLXE-NC heater like you used to with the pre LOT20 PLX-NC heaters?

Yes, the product can be placed in manual mode using the ConfigR app. When powered ON/OFF/ON it will maintain the specified set point. Used with the DWC , the maximum room temperature setpoint can be set and the room temperature maintained based on the external wall controller.