The rotor brake is on the floor, between the seats, just to the right of the center collective. Works like the parking brake of an old truck. Better have it engaged when you start them up so the blades don't take off and twist on you if the engine starts with too high an rpm.
Like others have said, when the blades are tracked & balanced properly, its quite a smooth ride, and the seats in the B2B are comfortable, even for longer flights.
I have several hundred hours in them and have some trips of 1200-1400 miles.
However, even though I have owned one for several years, I still think they are loud and ugly. But, its mine and I can fly and instruct whenever I want.