You shut down your computer the usual way, from the OS, then toggle the plug to restart it. In case the system hangs during shut down, you'd actually want to know that it's hanging, which you can actually see in the power readings of the plug.
> I’m not too concerned with safety
I'm sorry to state that, but that much is evident from the photos in the blog post (assuming you're author here). While the voltages may look safe to you, the whole contraption is safe just until something goes wrong. Examples:
1. You push around a dangling wire and short out a more powerful circuit.
2. Something on your dev board for development purposes releases the grey smoke. 500mA at 5v may seem low to you, but under the right circumstances might cause a fire. I don't see any fuses or other overcurrent protection in your schematic.
3. Your mainboard gives a defect and runs more that the expected voltages/currents to your dev board. God forbid AC from something else faulty in the electric installation (just saying because I've been zapped from touching the outside of a closed case).
4. Power surges, lightning strikes... Static electricity even...