I didn’t work on those but have worked on winglets for other aircraft. They make a big difference in efficiently. Easily pay for themselves. It is an expensive project as an add on. Besides the usual design, testing, analysis, and manufacturing you have what is called a “supplemental type certificate” to allow them to be used on the aircraft in question. All huge expenses.
I was amazed at how expensive everything was on a plane. Similar to a nuclear plant where you’re paying for testing & certification on parts.