I can tell you a couple of things:
The different kind of gas they are talking about is Brown's gas. It's the same as hydrogen and oxygen except the gases are in monatomic form and have not formed molecules (H2 and O2). I've written an article that you can read, "What Is Brown's Gas?
". It's very entry level data on the subject, not intended to give everything there is to know.
Brown's gas has been found my many users to be superior in it's ability to improve fuel mileage, so you definitely want to find a unit that provides a large percentage of this type of gas.
Second is that electronics packages that use a frequency tend to produce more gas with less energy if the frequency is tuned properly. It's my belief that this is due to causing the water molecules to vibrate, if the frequency of the electronics is a harmonic of the molecule's vibrational frequency, thus assisting the breaking up of the molecule into gas. However, this is my theory only based on the efficiency some of these units are able to attain.
But for sure, the better the efficiency (amount of gas per amp of current) will get you the better mileage.
Lastly, you can learn more about a vibrational electrolyser system from this article about how to build an electrolyser, found here
in pdf format.