The HiFiBerry power controller not only let you shutdown or start you power, but also includes its own microcontroller, rotary encoder and 3-color LED. The firmware sources can be found on Github. Power switching is handled by two low-resistance FET transistors to minimize the voltage drop on the power controller.
This is a beta test. There might still be some bugs in the software that will be fixed and improvements in the documentation to be made. Please have a look at the data sheet and our blog post before ordering the product.