In your video, the cyclist has his hand out throughout the approach, and the right turn, without stopping.
I can't imagine coming to a halt, being stationary, and starting away again all whilst continuing to hold out your hand. If you (like I) would return the hand to the bars, particularly during the starting away again, your indication is cancelled, or, at the very least, no longer displayed away from the body.
On a left turn, which generally are tighter turns, I'd imagine even less time for the indication to be displayed.
Well done for the idea, but I can't help thinking that there really isn't much point - maybe like wearing 2 cycle helmets, for added protection.....