I have not idea if it works or how it's supposed to work. However, it is apparently easy to misuse as there are quite a few law suits against hotels and various institutional massage providers (usually resorts) where patrons have received serious burns as a result of the apparent misuse of these products.
I listened to about five minutes of a thirty minute presentation from a lawyer who successfully litigated a case involving very serious burns, even some third degree burns. Among the factors that are important are the composition of the stones them selves (including their mineral inclusions), the temp they are heated to, how they are heated, whether they are allowed to cool, how they are applied (with or without towels), and whether the masseuse tests the stone's temp at all, and whether she uses her hand versus the forearm to test the temp (forearm is better). I didn't listen to the entire thing, but the bit I heard was interesting.
The single most interesting item was thats some well know and legit industry organization suggested 16 hours of hands on training before therapists were allowed to go work on members of the public. Yet in none of the cases he had seen, did a single therapist who had a claim against them have more than three hours. Even those who worked at big spas and hotels. Really a shocking stat.
Sounded like it the whole thing was an accident waiting to happen depending on how much attention to detail the person in question gave to things. I'll see if I can find any articles on it. Give that it was a lawyers only presentation, I doubt it.