BadNick

Unless I missed something, it seems to me it only does this...quoted from that link:
"The way our Performance Modules work is by sending a modified signal through a factory sensor in the engine compartment, called the IAT sensor. This signal alters the computer and the computer then reprograms itself for a more efficient air/fuel mixture."

So it seems to only change the "IAT" inlet air temperature signal to the computer, which will then change (increase) the air/fuel ratio since it is being "tricked" into thinking the air is less dense (hotter) than it really is...thus the engine runs leaner and you can get better gas milage. Running the engine lean can also make more power though beyond a certain limit it can be damaging.

To me this device seems oversimplified and potentially harmful...meaning that I really don't know if this will cause the motor to run "too lean" under some condition and that will cause damage, maybe slow and suble damage that you won't see right away. So unless I saw more data about how this effects the motor under varying operating conditions, I wouldn't risk it.

The better (but probably more expensive) way to do this would be to directly program the computer to run higher a/f ratio; there are aftermarket fuel computers that allow you to do this, but I'm not sure how well they've "cracked" the Mazda ECU's - but I would guess pretty well...most nominal factory cruising a/f's would be in the mid to upper 14 range, say about a/f = 14.7. You can usually safely increase that to mid 15's at low load cruising speeds, but the computer would still add necessary fuel under higher load conditions.

PS: I have such hardware/software on my Supra...which allows me to take the signal from my wideband O2 sensor and program any kind of a/f ratio I want. So even though my motor makes over 700hp when I hammer the throttle, I can get very high 20 mpg range cruising down the highway at 70mph....on the track under high loads I usually think in terms of gallons per minute.