The C63 M156 is relatively unique in how it was held back through a throttle restriction to make around 50-60hp less than the engine does in other OEM applications. Therefore, a simple remap is only unleashing the natural potential of the engine.
Having had mine both standard and remapped it's also not just about power, but how it drives. Standard the last 2.5krpm feels a bit flat, because it is as you hit the power plateau. Remapped there is a real zing to the redline that is much more exciting to experience and how an NA engine usually works.