I have one of those.
Yes they work.
I would certainly not say they are better than proper whetstones. If you have a seriously dull edge that you need to remove much metal from this is not a great choice.

However as a carry along sharpener they are fine.
It also will work to steel the edge if you drag it backwards from the way you use it to sharpen.

So:
Its not a replacement for the grinder, stones, hones and steel.

But:
It is a decent small sharpener for touching up a dull edge, it fits into a pack or pocket easily and it is quite light.

(and no, I do not work for them either)