A new board is available. It’s an easier-to-use version of the On/Off Board, with USB connectors and a 4-pin header for control and communication to your device. No soldering required.
Attach a microUSB cable to the input, and a USB cable or adapter between the output and your device. Power the board on using a momentary switch on two of the header pins, and the other two pins run to GPIO pins on the Raspberry Pi (or any other device with GPIO). If you don’t want to use software, holding the switch for a few seconds will power the board off. It can also automatically power off the Raspberry Pi after shutdown, using the same software from the original On/Off Board.