I've seen this tornado thing for many years now, and I'm suprised that it's lasted this long. That must mean that it works for people right? Or they've done a great job marketing this thing, whether it works or not.
My $0.02 just so I can put the Mech Engr degree to use for something that interests me...
Air does flow at a much higher rate with lower restriction/turbulence if it can move through a circular x-sect in swirls, eddies, or vortices. Just like the water going down your sink will naturally flow in a minimal resistance pattern-swirl.
The tornado takes the air after it passes the filter and promotes a swirl pattern of flow-definitely increasing the potential velocity on the way to the throttle. However, this swirl can't really hold its form through the throttle plate, even if it's wide open. Additionally, you can't hold a swirl through the highly turbulent intake plenum, where all the air gets split into the 6 runners.
Therefore, it all depends on where the bottleneck in the system is. It could be at the filter/afm, throttle body, or intake plenum, or intake ports on the head (generally). If the natural airflow botteneck occurs between the filter/afm and throttle, then you can expect gains by swirling the air between these two points with the tornado. It all depends on the particular engine and intake system.
The other point is that in theory, it should only work at relatively high flow rates. At low airflow it could even present a restriction since there isn't that much turbulence to reduce. I believe all their testing is done at some RPM that is near redline for their test vehicles- some tricky marketing if you ask me.
I'd say that if you own the exact car they did testing on, then dump the $70 and give it a shot. Otherwise, I think there's prob some better ways to spend the cash.
