The OnOff Controller basically uses the same hardware design as the Level Controller. By changing the firmware, the triac is only switched fully ON or fully OFF. Also the type of zigbee device is changed: it can be programmed as a On/Off Output (DeviceId = 0x0002) or as a On/Off Light (DeviceId = 0x0100). The output can be switched/toggled by a zigbee command or the 2 buttons on the unit (one for Off and one for On).
In addition the output can also be toggled by an existing wall switch (black wire connected to 220V or to nothing). Via a opto coupler the micro controller is informed about the presence or absence of the 220 V/50 Hz signal and toggles the output.
I have used this device to switch on a led ceiling light. Here are some pictures of the construction of this light: