a community of practitioners
I tried it in a spa I used to work in. We never had a course on it.The shells have a hole where you put a tea bag looking product that chemically reacts to produce heat for an hour or more. Once its been used you remove it and you can repeatedly reapply new "bags" which would be repurchased hopefully to increase sales.. You can use it like Hot Stones but at most two at a time...It remains hot although if I remember correctly it lost heat as you moved it so it was good to have another. The second could reheat itself as it sat idle.. I noticed when turning it in a certain position it leaked liquid..Also trying to remove the bag often cracked the edge of the hole entrance. For this and other reasons our spa didn't decide to keep it.
As a gimmick to sell to clients..it has to be your decision . but as I see it gimmicks might appeal to a person who wants to wow..someone else. as in Valentine's etc.with something new and different..but may lose its intrigue after the first or second time. For the most part I believe it may be inventory that would cost you more than it made for you.Although this was my experience with it. Perhaps others had better results. Good Luck