Yes, I'd seen this one on my travels around the web. Right idea but probably not substantial enough for a patio door - or wide enough, as the door is 8 cm. And I suspect the easily removable sticky fixing pad might not last beyond the first downpour.
I did love the write-up though. "Simple but magical". Also, and this nearly sold it to me, "No accident: there are always accidents when you squat to keep the traditional one in place..."
Personally, I'm always having accidents when I squat, and I never squat so often as when I'm trying to hold a door open. Or maybe 'squatting to keep the traditional one in place' is a euphemism.