Hi,
I have done both hot stone training (about 6 years ago) and Lava shell training about 15 months ago, and I have to say that Lava shells are my favourite...the concept is so simple but it totally works and provides ease of use for the therapist ( I do abit of mobile work and you definately can't do stones mobile) and a totally relaxing treatment for the client without constantly breaking contact to "find" stones in the heater. The shells stay hot for an hour and once you have grasped the heat control (doesnt take long and they go through it in loads of detail on the course) it is amazing, I really enjoy doing the Lava shell treatment, and have had very positive feedback from clients. They have recently launched the cold shells now, and provide a detox massage course, which sounds very interesting, I am looking to do this once I have some spare pennies!
Hope this info helps...