WHOA! You should get 30 of them at that price. Yowzers. Just search for "whiskey stones."
They work, but they don't chill as well as an equivalent amount of ice, so you need a bunch of them in a glass. A package of 9 is only good for a couple of glasses if you want it good and chilly. Aside from that, they don't seem to change the taste at all. I say they work as advertised, are rather novel, and are worth the $20.