Trevor,
Considor the cost of building a motor with the same performance spec's & you'll see how cheap this really is. As long as your motor is in spec, this is a bolt on adder yielding as much as 50% HP & torque gains. All this is at 5-6 lbs of boost. With a low compression motor (8:1 or lower) you could go to 9-10 lbs for street use on 93 oct gas & some ignition enhancements.
The beauty behind this is the car runs on one SU carb. Around town you essentially drive a stock car. Only when you step into it does the by-pass valve close allowing boost to build. You have power on demand, not wasted power. There is no need to drive all day with 9.5:1 compression, loppie cam & over carburetion.