the problem with compressed air: you run out of it, and it doesn't INCREASE in pressure. The problem with electric super/turbo/de-duper chargers... it maxes out from the start and becomes a restriction.
turbos and superchargers function on compounding either pressure or engine speed. On a turbo, the exhaust determines shaft speed. as the exhaust moves faster, so does the turbo... it just keeps going and going. On a belt driven supercharger, as the engine speed increases, pressure increases. As pressure increases, the engine speed increases at a greater rate and creates more boost.
It's just so much easier to build a properly functioning turbo setup.
edit: but yeah seriously, if they claim 900+ watts, then we're talking around a 70amp load during motor activation. Talk about an unnecessary load on the alternator!