By far the most frustrating thing about plastering jobs is the drying times. This is especially true with inside corners - with a knife you pretty much can’t do both sides the same day because you’ll always end up messing up the opposite one.
I finally gave one of those corner tools a try, and the result is fucking mint. The customer is going to be so happy with these flawless corners tucked behind the curtains in their living room.


See, that’s the part I was expecting the corner tool to make easier. If I’ve got to feather the edge with a normal knife anyway, I might as well just use the normal one for the whole thing.
but then you have a sharp internal corner
if that works for you, then yeah no point using this