They are basically junk.
They can't shoot the blade very far at all, with any power. Just a few feet, even with the most powerful spring you can find to put in it.
Even with that, it can barely pierce an inch or so into a simple cardboard box at 5 feet. And maybe it might even bounce off of it too. The speed/energy of the blade depletes so rapidly, that it's only even halfway passable at ranges which you could reach with your arms and a knife in your hand, anyway.
It's a great fantasy knife for a person to imagine that it actually does something. As anything else, it's essentially worthless.