The thing that stands out most when I look at these images, is...

The thing that stands out most when I look at these images, is firstly three or more tethers should make it possible to deploy the buoys in much shallower water than for a single tethered device.

Secondly, the side to side movement of the buoys will not be as great.  That should mean that they can be grouped more tightly.

It will be interesting to see how multiple tethers alters the motion of the buoys.  To me it would seem that the motion will differ from the smooth circular motion of a single tether device, to a more pulsating and erratic motion as the tension on each of the tethers changes.

How that translates to energy capture, must be the reason for these changes.