Kinda all answers are correct
I had a LONG chat to the 'boys in brazil' on this subject. It started when i asked why CRJ's have them and ERJ's dont. Short answer was that the added weight , cost and complexity didn't justify the small reduction in fuel flow (Anti ice system for these things can be a bitch). For flights LESS than 7 hrs, they are not viable.
I also remember a discussion at SAA on the 744 that lost 1 winglet. The Boeing CDL also gave increased fuel flow and reduced MTOW. However on landing, the trip was sent off to SITA and they reported the aircraft had shown NO DIFFERENCE in fuel burn. However, cause the aircraft in question was Lufthansa, this is a 2nd hand story.
I remember chatting to a 738 captain when half the fleet had winglets and half didnt. He said that the trip fuel was the same for those with and those without. But again, largely used on short haul trips.
A few months later, on seeing the Legacy, i called EMBRAER again and asked if they were about to say sorry for changing there minds. And when the retro fit kit would be out for the ERJ135.
Answer was that NO retro fit. Not worth the effort, and that on the Legacy, they were fitted as most costumers THOUGHT that they were a cool fuel saving idea. ERGO the buyers wanted 'go faster strips'. So they fitted them, even though the benifit was marginal over the aircraft's mission profile.