Thanks for the video link, Darren. It illustrates very clearly how vital it is to get any kind of drogue to sink well below the surface. A drogue that's in the frothy, tumbling top of a wave is no use at all. I see that when they used a length of chain, it looked like about 5 metres of 8mm or 10mm, which would weigh about 7 - 10kg. That isn't enough. The JSD website has an illustration showing a 30lb weight well below the surface, but that's only a hand-drawn picture. To do any good, I'd want to see a weight equal to the weight of the boat's main anchor - about 20kg in the case of that test boat, at a guess. In fact, a scoop, plough or claw anchor would have something of a paravane effect, drawing the drogue deeper, as well as stabilising it against yaw and rotation, so this ought to be the necessary weight, IMHO.
Not enough attention was paid to launching the drogues, with the result that some of them got tangled and didn't deploy properly.
And another thing that's graphically illustrated is just what a PITA it is to recover a JSD.