The S76 rotor brake starts off with a partial application, and then goes to full on at a lower rpm (I can't recall the exact numbers offhand, it's been a couple of years since I flew them). The standard application is to engage the brake with one engine out and the other at idle. It won't actually engage until the rotor slows. It does slow quickly, but the problem is engaging at low speeds, not having a constant engagement. As long as the deceleration is constant there should be no damage.