A little pricey, but great to relieve back tension/knots
I really like the ability to apply firm pressure to a specific point on my back without worrying about dropping the ball when I'm done and having to chase it across the room! The "tail" (rope) is also great to help with positioning. A handy person could make this themselves for about 1/3 the cost, though.
This is great because it doesn't fall. I thought I would want the ball at the end of the rope, but it turns out that it works much better with the end of a rope in each hand. Great tool.