Winglets seem a good idear.
But do have some draw backs the older NG73's and 75's with winglets have noticed a reduction in life of the wing spar due to the extra flexing. Been told the problem has been addressed with the newer 73's but to what degree I am unsure,
Winglets saves money on fuel burn in the short turm but does it shrorten the life of the airframe?
Can now see what some airlines have not gone for this option.