The advantages and disadvantage of a McKibben actuator can be briefly summarized as the following:
High power density (force output relative to size).
Low weight and good power-to-weight ratio.
Scaleable to human scale sizes, such as for use in exoskeletons or assisted movement devices.
High compliance (low stiffness) if using liquid hydraulics, allowing for high-frequency applications.
Easy to control using electronically-controlled pumps and valves.
Good strains of around 10%.
Relatively simple to fabricate.
Reliance on fluid pressure limits use in abnormal pressure environments, such as undersea or high altitudes.
Lower power efficiency, due to gas absorption of energy as it expands.
This also creates time delays between input (when pressurized air is released) and actuation (when the pressurized air completely fills the balloon).
Dependent on an external source of pressurized fluid -- either a compressor, or a bulky tank.
This will reduce the effective power-to-weight ratio of the actuator, and becomes worse the larger the actuator gets!
Loss of gas pressure releases tension very quickly -- this will cause the actuator to "snap" back, and potentially suffer damage if it is mounted to a large load.