What's the difference? Obviously, the full hydro is self-contained and uses some sort of motor to generate line pressure.....I'm assuming that the air-over-hydro uses the air pressure from a seperate compressor to achieve the same result??? Is one considered "superior" to the other in terms of speed, accuracy, repeatability of bends, better "feel" and control, etc??? I have a very nice upright compressor (60Gal, 4-cylinder) that's got plenty of SCFMs for almost anything.... would an air-driven system be simpler (pronounced: cheaper) to build???