[jspatz1]

It is simply a linear actuator that works by shortening as the rubber section "balloons" with air pressure. It differs from a cylinder in these ways: Can only pull, not push; much more force than a cylinder of a similar diameter; less range (stroke) than a cylinder of similar length. It is also said to be faster and more "sensative" than a cylinder, probably because of the lack of friction and moving parts. Its application would limited to a situation where you needed a strong, short pulling force, with a minimal diameter device.