Successfully used this product to stop my 5 year old son from sucking his thumb. They currently have a school holiday promotion, 25% off. I paid $99.95 plus postage, with the Promo code, it comes down to ~ $75 + postage.
According to them:
"How does Thumbs Out work?
The theory behind the Thumbs Out products is 2 fold. The first is that thumb sucking is a habit, and a habit can be broken if stopped for a period of time. The second is that the product itself hinders the enjoyment given by the sucking. When sucking a thumb a seal is created around the thumb by the lips. This creates a pleasurable sensation, perhaps going back to that initial feeding time when tiny babies. Children can still physically suck their thumbs, or fingers, however the enjoyment they once received is gone as there is no longer a seal. Once you no longer receive the pleasure, there is no point continuing the action. Hence, thumb or finger sucking is no longer a problem."
We used it all the time, over a few weeks, during last school holidays, and then only at nighttime. He was starting to get a buck teeth look from his sucking. The dentist told us we'd be up for orthodontic bills if we didn't stop his thumb sucking soon. This, and over 2 weeks of reward charts, has had our young fella stop this habit.