Skpotamus
Brown Belt
But "valid" is a judgment call that's made by others, after the fact.
Unfortunately, this is true with all SD situations. Whether you use a knife, a gun, a brick, a rock, a tree branch or just your bare hands, some holier than thou posecutor or LEO can decide that you weren't "valid" and go after you for it.
From what I've seen, if you're justified in your use of force, whatever you use isn't really important. It's making sure you were justified that is the tricky part.