I wouldn't say a waste of money, just too much of a fag.
A fag to set up and a fag to use - especially with a longer blade or a thick blade.
They look like a great idea and I know some people like them, I just can't be bothered with them. By the time you've set the thing up I can have finished sharpening my blade using my sharpmaker which I use on all my knives including kitchen knives.
