Beam still has to be in the direction of the mic, which wouldn't help if your body is blocking most of the direct waves. You get some scattering, sure, but I think ultrasonic is pretty absorbable, right?
But the same is also true for rotating the bracelet isn't it?
The bracelet does not have directional speakers, so the ultrasonic waves will kind of spread everywhere, bouncing off hard surfaces, and ultimately reaches the eavesdropping device.