"The main and most important feature of this case is an amp. It features J-FET OP-AMP to provide Vacuum Tube like sound output with 180mW output power. To enjoy that power all you have to do is press a button on the side of the case. You also get a touch-panel on the front to control volume, which is quite nice. The amp provides higher volume, as well as a broader range for music. Everything feels much richer: be it classical instruments, Drum and Bass or Vocals. The end result is a much richer experience then what you would get with the stock iPhone."
David - iPhoneWorld
You can read David's full commentary on Auzentech's excellent i.Fuzen HP1 now available from Mittoni.