Basically tuners like MSD's to increase spark. They open up the plug gap and with 9mm wires, advanced timing, boost or NOS see a benefit. They also run high flow exhaust and intake mods. You need higher fuel, air and flow ratios to need race rated spark that helps prevent fuel fouling the plugs.

Without the other mods, as jhodg mentions, they just eat ignition parts. Mercedes do not have tuner or an aftermarket parts following 'cause the engineers kind of know what they're doing. Others can't do things better.