It's an unlock and people see it as a way to either call TF2 an RPG or call it a bad weapon. The only thing is, it's only got the 2 shots, which WOULD make it a weapon for tools, but it has fast reload time.
The targe, now that is a weapon for tools. Kill 1 person with it, and then what? I don't know why people don't use stickies, they are almost like a key component to the demoman.