Its a 69 cent radio shack resistor that fools the ECU into leaning out the mix in the cylinders. Your paying 5.31 for the instructions on how to do it.
You will NOT get anywhere near 22.5 HP though, maybe 5 HP? I wouldn't recommend it without a tool to monitor the A/F mix, because you have no idea what's going on in those cylinders. What if you install it wrong? What if the guy used too much or too little resistance? Damage could be done. This type of thing is not really snake oil, because some people have posted small gains on other vehicles. If you ask me though, its like a poor man's APEXi, and unless you know what your doing, its not worth the risk.
I think Green has a very good point singy..... Since this chip screws with the computer in the car.... Would you want a 69 cent chip possibly screwin up your engine and then for some god forsaken reason Mazda telling you that because this was added that they won’t cover it under warranty because this chip was added? I wouldn't take that chance with my engine!
The Apex'i would take some tuning and just overides the ECU. If you want to spend that kind of money, hold off for the Diablo Predator ECU programmer. That'll let you directly reprogram the a/f map. Plus, you'll be able to eliminate/raise the speed limiter.