For an elastic air brake at each of the blade tips, the whole blade is active, so the airbrake has to destroy all power generated by the rotor as the system has to work also for an unloaded generator. The field tests have been performed for an unloaded rotor. The blade speed is maximal at the blade tip so you need only a small air brake area to generate a lot of drag. The air brake was made out of 1 mm stainless spring steel and had a chord of 200 mm (the same as the blade) and a width of 150 mm. The air brake was connected to the blade at the front side and bent outwards due to the centrifugal force acting on it. It produced a very large tip vortex which sounded like a helicopter was coming over.
If you turn only the blade tip, a smaller remaining part of the blade is active than for an air brake at the blade tip but this active part of the blade will still generate a lot of power. This power can only be destroyed for a small blade tip if this blade tip is stalling. So you need negative pitch control for the blade tip. A stalling blade tip will also be very noisy, probably less noisy than my elastic air brakes but I won't chose this option if you have neighbours.
The advantage of positive pitch control of the whole blade is that the lift coefficient of the whole blade is reduced and so there is no part of the blade which generates a lot of energy which has to be destroyed by another part of the blade. Negative pitch control of the whole blade can also be rather noisy but it can be used for constant chord blades as for those blades, stalling starts at the blade root. This is because for those blades, the lift coefficient is low at the blade tip and high at the blade root.
In about 1980 there has been a France company (I can't remember the name) which supplied a windmill with a rather big 2-bladed rotor with negative pitch control. They used a clever pitch control mechanism with two springs in it with different stiffness. This made that the blade angle was large during starting and the weak spring was compressed already at low rpm which makes that the rotor was turning with the normal blade angle at moderate wind speeds. At high rotational speeds, so at high wind speeds, the strong spring was compressed and then the whole blade was stalling. So an advantage of negative pitch control is that you can have a large blade angle during starting if you use two springs with different stiffness.