It has zinc stearate in it - I have no idea what "stearate" is or its health implications, but zinc, while toxic in very large regular doses, is a necessary nutrient, and since the degradations of most of the soils our food it grown on, most of the world's population is running at a slight zinc deficiency (it is implicated in a big way in colds and flu, depression, cancer and all sorts of other things that are becoming a lot more frequent than they used to be).
Perhaps it tastes attractive to your cat because whatever you feed him isn't all that rich in naturally occurring zinc. I know that about the largest source of zinc in my diet is oysters, which are very rich in the stuff indeed - but I haven't eaten oysters in over two years. <sigh>
Perhaps I should eat fanning powder.