This product was discussed on numerous websites, and on each one I've read, the consensus is that the magnets do absolutely nothing. And it doesn't even make sense.
Magnets are considered magical elixirs for countless things, and it is likely that somebody's trying to make a buck on people that look for a quick, inexpensive performance booster. I've done some searching on the internet, and I have found nobody referencing any technical literature that proves this concept works.
On some Magnet websites, there is info on how a similar product will help soften water by polarizing calcium crystals, preventing them from adhering to surfaces. These sites show proof that it does work for this purpose in recirculating systems such as swimming pool heaters. These sites mention magnet use in auto fuel systems, but don't make the same claims.