[cdancette]

They are basically inflating and deflating balloons filled with some flexible structure.

So 1000x might not be that impressive, because they are very lightweight.

And I guess it requires a big pumping device in addition to the muscle (which weight is not included in the calculation, but certainly should be).

[blacksmith_tb]

The weight of the compressor is important, but one compressor could be driving lots of 'muscles' via opening and closing valves, so it isn't completely disingenuous. It's analogous to, say, a robot with six motors, all powered from a single battery.

[arghwhat]

A compressor driving more of these hydraulic actuators need to be larger and heavier than one driving one hydraulic actuator.

Rather than battery and many motors, its more like motor with many transmissions and clutches. Vacuum is also a bad choice of medium... It requires stronger pumps, stronger hoses, better seals, etc.