"...It's absolutely useless..."

It does leave a little bit to be desired. I can make sparks with one, but there are better choices.

The back of some knives are worse that that little thingy. If they don't have a nice sharp angle on them (and many don't), they won't even make one little spark. If you are going to rely on your knife (not the cutting edge) for use with a ferro rod, make sure you try it first...