Firstly, standard Aero spokes are fixed, which means that they do not perform at optimum when there are changes in bike or wind direction or angle. With the new "Rotospoke", it adjusts its position according to the direction of maximum air pressure, therefore reducing drag. Supposedly this is by around 10%.
Secondly, as the spoke reaches the bottom of its travel, the hollow part of the "U" acts as an air collector increasing rotational force. The potential increase in efficiency has not yet been calculated.
There are also some cool side-effects as the spoke also makes noises at different speeds, very similar to those of animals. One of the Dutch Engineers, Mr. B.O. Gus commented "we are confident that we can reproduce most animal noises quite accurately, including lions, hyenas, dogs, cows, parrots and pigs".
"However there are some doubts whether we can get competition approval, as with a group of several hundred riders there could be a serious noise issue".
We await further news...