First off, I am extremely doubtful about "zero emissions" part.

BUT, it would be interesting to see if they are actually doing something like using compressed air as a means of energy storage - instead of charging a battery like in a typical hybrid.

Batteries are not very good at soaking in large amounts of energy in short amounts of time - exactly what happens during regenerative breaking. But me thinks it would be significantly more efficient to absorb that energy spike as compressed air via on-board compressor.

If that gives them better fuel economy than gas-electric hybrid then this would be the thing to watch.