There is so much bad information/guessing going on in this thread its incredible. DEATH_INC is the only one that really understands whats going on.
First off, yes, this mod works. Its only good for a few Hp, but it does work. Most racing organizations don't allow this because it has the opportunity to dump oil on track, or at least create a lot of oil smoke if the engine is filled too much and pukes oil into the exhaust.
You don't need to add check valves to the exhaust, the reed valves do that. Think of the reed valves as diodes that only allow air to go one way, into the exhaust. Vacuum is created by the negative pulses in the exhaust. Since the exhaust is always flowing, the pulses are always there creating vacuum regardless of throttle position. The vacuum created by these pulses pulls the reed open, and when the pulse loses its energy, the reed closes. Since drag racers use this, and they're on the gas 100 percent of the pass, that should be some kind of clue that full throttle conditions create vacuum.
The air switching valve is not a "pump", its merely an air switch, hence its name. The ecu controls the switch and allows filtered air from the air box past the reed valves and into the exhaust to provide extra air to burn the unburned hydrocarbons that managed to get past the combustion process.
Hope this clears up some misunderstandings.