I have being suffering from a damaged disc and trapped nerves in my neck and back for a while, and have had numerous physio sessions over the past few months.
I bought this out of desparation more than anything but the results were remarkable. The second time I used it, there was a sequence of clicks down my spine and a huge amount of tension and pressure just disappeared. Okay, I couldn't get off of the thing and had to roll myself onto the floor sideways, but my back is much improved!
I'm not going to claim that this product is a miracle worker, the success of any medical product will relate to the specific circumstances of the ailment, and in my case I also had intensive physiotherapy, but to me its certainly been a huge benefit.
If you have a bad back, it's well worth the money to give it a go.