I have the feeling that technologies like this (including these kites and also Flettner sails) are too little too late. While a 20% saving on fuel is great news for the operators of these ships (if the sails themselves are low-maintenance), the world as a whole seems to be moving off carbohydrates in the next two decades. For shipping this inevitably means to switch to green fuels (e.g., Ammonia). Once the production of such fuels has reached a certain scale, sails might not be necessary anymore.

The reason here is the extremely low cost of energy from photovoltaics: We see less than $0.03 per kwh [projected prices for some currently planned large scale farms] - that's about $0.3 for the energy of 1 kg of bunker oil. Bunker oil sells for about $300 to $500 per ton, so roughly $0.4 per kg. That means that a replacement fuel with more than 66% conversion efficiency could already be competitive right now. High Temperatur Hydrogen Electrolysis is reportedly available with 80% energy efficiency. As far as I know, there is no indication that solar costs could stop falling anytime soon, so in the next 20 years we will probably see it drop well below $0.01. So if I did not misplace a decimal somewhere, the future should be in relatively cheap large-scale green fuel.