There are two systems, EBS and SBS.

EBS is emergency brake assist, and I wouldn't worry about that as much. It applies more brake force than you do, if you hit the pedal fast.

SBS is another story. In normal operation (not fail-safe), it applies the brakes for you. There's a sensor that determines the pedal movement, and the computer runs the brakes. The computer also closes the valves between the master cylinder and the brakes, so the master cylinder itself provides no fluid pressure. In fail-safe mode, these valves are open, and the master cylinder provides pressure to the front brakes only.

SBS looks to be a nice system, as long as the eletronics work properly. It provides pressure to the individual calipers as needed, using the wheel speed sensors. But MB is not known for the reliability of its electronic systems, so I'd steer clear of SBS brakes. Also, with SBS, you must deactivate the system to work on the brakes. This takes the Star diagnositic tool or a special tool just for that job, which costs about US $200.