The advantage of the kites they demonstrate here is that they leave the deck of the boat much more free for cargo than traditional sails. There have been a few 'low footprint' wind power startups for shipping but from the purely financial perspective the lost cargo volume has never yet been worth the fuel savings. Using a kite that consumes no cargo capacity could actually help an eco-technology be adopted by these shipping companies if it helps their bottom line.
In the right context, leather goods are much more durable and sustainable than synthetic alternatives. That said, leather is a co-product of the meat and dairy industry which is currently ridiculously unsustainable. Leather for leathers sake in designer goods and such is ridiculous.