Absolute snake oil. The whole idea behind an ignition coil is to be a "step up transformer" and convert the ~13.8 volts to over 50,000 volts so it can overcome the air gap in the spark plug. It
is true that a weak charging system can result in a weak spark, but limiting the maximum voltage will do nothing but limit the maximum output of the coils. It wouldn't hurt anything electronic (like the bike's ignition computer) to have a stable supply, but they already have regulators built into them to arrange this.
Speaking of which, if you REALLY want to try this on your bike, don't spend US$99 on a "magix box", spend about $3 on a 13 volt regulator from any electronics store.
Matt
