It's a load of shite.
If it made that much difference, then the PHD bods at audi would be adding this to the car, not some cheap looking web-site
Basically, these modules 'trick' the ECU by cahnging the signal from the MAF (Mass Air-Flow) sensor. They do not make the car any more powerful, but do change how it responds to throttle input, making the car add less fuel and advance the timing more by thinking it is getting a different amount of air than it is (effectively offsetting the mapping)... It may feel 'racier' but at the end of the day it's no faster or more powerful but it is running hotter exhaust gasses and adding nasty stuff to the exhaust which will destroy your Lambda sensor after 20k miles.
...That's just my humble opinion of course.