My sister picked one of these up from Freecycle.
When she got it, she used it a lot, but like the people who bought it originally.....it eventually sat in the garage collecting dust. She claimed that when she used it in the beginning, it really helped. I think it was just a pain to get in and out of.
I tried it for the fun of it and it did relieve stress in my back. It was kind of a cool feeling, but I'd rather locate a massage therapy school and get $20 massages instead of wasting money on that piece of equipment.