Yep US amps are hella sweet, but unless you have a awsome electrical system, you won't see the power from those amps. Us amsp have unregulated power suplies, which means their power output is related to the voltage and current input. Theese amps are the way to go if you have several or a high output alternator and several deep cycle batteries to go with. A typical class D amp can draw as much a 2 times less the current of an unregulated ab amp, with similar power output, and similar voltage and current imput. Us amp are the way to go if you have the cash needed to make them work up to their potential..eg..killer electrical system..US amp have excellent specs on their equipment, but without the proper electrical setup in your car, they would be a waste of money IMO. Those are great cheater amps too if you like to compete sice they are way underated. A simple trick of upping your voltage to 16-18 volts will give awsome results, but at some expense of the needed equipment to do so. The best bang for the buck will always be the class D amps, because of their efficiency, and cost, output power, and input voltage and current they require...