Does seem like a good idea to save a bit of time and prevent mess.
Looks a little like a bayonet fitting for a gas cooker, so there could be issues with it re seating after the last dregs of dirty oil come out. I suppose the cap would stop it leaking out if it didn’t re seat. Imagine if the spring popped out and went into the pan though :?
A nice idea but I prefer a proper plug, even if it does mean a burnt wrist every now and then :roll: