As a newbie to drywalling, I experimented with those rigid corners for INSIDE corners as a way to make the job easier. It didn't work as expected and I found that for me, using tape was simpler, less messy, and much more sure thing. Especially when using a right angle knife.
But it makes me curious, what are those rigid corner dealies for?
Let's make sure of what I'm talking about, I am NOT referring to those metal corner plates that you install where two sheets of drywall come together to form an outside corner. I'm referring to the metal or plastic plates that are used for inside corners.