There are two approaches. One is an ECM Reprogramming which alters the way that the computer controls the functions of your engine. Companies are working on this now, but it costs more than twenty bucks.
I do not know of the specific link or product that you found, but I do know that there are lots of products that sell for around twenty bucks or less that are supposed to do miracle things to your performance and/or fuel economy. Magnets to "align" your fuel molecules. Spinners to create "a fuel mix vortex" in your throttle body. Chips to make your car "become hyper-fuel efficient."
The claim is usually that "the man" doesn't want you to have these top-secret technologies, be they GM or the oil companies or the government or whoever. The real conspiracy, though, is usually among the people selling this junk. Twenty bucks is small enough that you are not likely to pursue the matter if it does nothing, but large enough that if a lot of people buy this crap that you can make a handy profit.
From a business sense, if GM could put a $20 gizmo on a car to improve horsepower by 30%, wouldn't they do that? Imagine a SKY that cost $20 more but that could blow away a MX-5s performance. GM would market that in a heartbeat. 50HP for $20? No brainer.
In reality, most improvements result in far smaller gains for a much larger expenditure. 10HP at the expense of a $700 performance exhaust system, for example. GM, in that case, might go with a slightly less efficient exhaust to knock several hundred dollars off the price of the car. If you are willing to pay more to get the boost, then you can upgrade at your own expense (and people do - like me.)
But to think that there is a "miracle" to get you a massive power boost for just a couple of bucks - that is more likely to increase the seller's bank account than it is to increase your horsepower.
Be careful. Be very, very careful.