I'm sure he'll weigh in here, but here is my understanding of the system.

The Sensotronic brake system has no master cylinder. The pedal no longer mechanically actuates the brakes. Rather, the computer senses the pedal movement and pressure and applies the brakes for you.

Because it's computer controlled, there is a high-pressure reservoir (something like 2000psi). It needs to be depressurized before dismantling any brake parts, and repressurized before driving the car after repairs.

If you search here for "Sensotronic" you will find a thread linking to a less-expensive tool to deactivate and reactivate the system. Around $200, IIRC (this may be the SDB 102). Still, at this time, I would be extremely uncomfortable with electronically-controlled brakes.