Oh,
Well they added it in early 07 and I have no Knowledge of the "factory" option, but I bet the after market choices are less expensive and they have been around for years so also probably they are perfected.

Viper and Hornet are the brands I have on my cars. Those include a few options, but I think you can get just the starter installed for around 250, based on what I paid for the whole package.

It is wise to talk to the installer and find one with Mercedes wiring experience so that they don't screw up the car.

I've had mine five years in one car and the most recent installed in October, I have never had a problem with the brands I have.

Good luck on your choice.
RP