An iteresting idea, but I have several reservations..
One that is addressed on the website, is the danger of transporting around a cylinder of air compressed initially to 4000psi.. do you notice the trucks carrying compressed-gas cylinders around?? They carry Oxygen, Argon, Helium, Acetylene[slightly different storage medium], propane and other high pressure gasses.. There are a LOT of DOT safety regs involved in transporting high pressure gasses..
Another issue will the the dangers of filling the tanks, the compressors, hoses, hose connections etc... all very dangerous.
And now the real killer. at least in my mind what kills the whole deal... what is the REAL cost to compress air to 3-4000#?? You need to turn that compressor with some type of motor or engine.. either electric or a fossil fuel burning engine..
So every time you convert from one form of power, to another there are losses because the conversion is not 100% efficient... I used to to a lot of metal fabrication.. I love air powered drills, hammers, chisels, and high speed cut-off tools and grinders.... BUT.. my electric bill was astronomical.. I even though to try a different 'higher efficiency' air compressor... but the answer was to go back to electric drill motors, electric grinders, and use electricity directly as much as possible, instead of using the electricity converted to air, converted to motion for the tools..
So unless you get your electricity and therefore your pumping power for very cheap,, the actuall cost to fill and use these vehicles may be higher than anticipated...
HOWEVER:: for a municipal fleet, or a factory, or in a city with very cheap power,,, this iooks like a really neat idea !!!