The disc was too light to create sufficient gyroscopic effect to notice. The disc had a central anodised aluminium knurled knob so as to unscrew the disc from the frame. The frame itself was strapped around the helmet with strong elastic, and being in two parts, was able to pivot up out of the way if needed (Both images show it pivoted up). It was also backed with a firm rubber of some sort so as to prevent the whole thing being blown up and away. Never had any problems with it flying off.
The biggest drawback was looking like you had a windmill on your head - small boys would be quick to point this out . . .