As far as I know they do work.
My guess is that the metal surface simply works as a catalyst and breaks up "smelly" molecules (such as sulfur compounds). Metal catalysts are often used for this purpose so it is at least a plausible explanation.
Note, however, that ANY piece of stainless steel (with the usual elements: Fe, Cr etc) should work equally well. Although washing your hand with a fork might be a bit awkward.