My understanding of the thing is that it increases the voltage going to your spark plugs.
I don't know about this specific product, but my best guess is that it's probably a Capacitive Discharge Ignition amplifier. Such a device uses capacitors to store a charge, then releases it into the primary windings of the ignition coil(s). This type of ignition uses the coil(s) as a transformer, yielding a hotter spark, yet at a shorter event duration. This is as opposed to a normal inductive coil fired ignition, which builds a magnetic field in the primary windings which induces a current and voltage potential in the secondary windings when the voltage in the primary windings is removed, thus collapsing the field and creating the spark. Both work good, last a long time.
More power means you can get a longer spark and use a larger gap for more positive ingition of the mixture. Since there is a supposedly large increase in voltage, you should use low resistance spark plugs.
I believe most all motorcycle spark plugs are of the low-resistance variety, as opposed to the resistor type plugs that are/were common in automotive aplications. This would be due to the fact that they are/were helpful in attenuating RFI that made radio reception and ECU operation a bit frustrating. Since these bikes depend on a computer to run, I don't think I'd risk creating an RFI problem in hopes that I'll find an extra HP or two. YMMV
Twins generally make best power when they're run rich, and a better spark may free a pony or two. But I doubt if you'll get any more power. However, properly installed, the bike should run smoother.
I'm gonna bite on the remark about twins making best power running rich. Just how rich are we talking here? I'd venture a guess that around 13.4 to 13.7 to 1 is close to ideal on these engines, as it seems to be on most NA engines. Are you suggesting that it be richer than that? I'm curious, this is not a flame, what have you seen/heard?