There are lots of grand claims for the potential of wind assist on ships, but I suspect they're based on idealized physics and best cases. Actual results seem to be less impressive https://www.ics-shipping.org/news-item/potential-of-wind-assisted-propulsion-hindered-by-perception-and-funding-challenges/

They claim 5-10% fuel savings, which is decent, but not earth shattering. Pyxis, which started operation in August with two big wing-sails, is likely to be the best current practical evidence, but I haven't been able to find any results online. Speculation that it might reduce fuel consumption by 3 tons/day, which is about what you could get just by slow steaming.