We have on good authority from a friend that these things work really well. The idea: You heat the granite disk in the oven or freeze it in the freezer, and it will keep hot things hot and cold things cold. Might be a good idea to keep something chilly at an outdoor summer party.We do always get frustrated when we serve ice cream at a dinner party and it melts while everyone's waiting to be served. And if you have a family member who wants his or her food hot until the last bite, this would be a great gift.
Actually, we think the best use would be like a hot plate; set serving dishes on them to keep the extra warm or cool while you serve/eat dinner.
Our only gripe is the cost. Large stones are $60 each; small ones are $40. You can choose different colors of granite, though.