Logic trigger like shorting pins on the Pi itself versus turning on/off the power supply? Either should work, I think. If I've got everything right, the OS running on the Pi should always shut down before power is cut.
Because I didn't know they existed 
. That said, I'm looking into these and it looks like all of them require a phone app or an internet connection or both? I'm looking to write some scripts on my Desktop computer that will power the Pi back up when I need it, and I absolutely do not want any part of this to require a connection to an outside network.