I think you are right in that the high tech tips are'nt all positive. With a light load and at high speeds (and airliners fly at high speeds) the parasitic drag from the wing tip devices will most likely be too too high to be of any overall advantage. Heavy...?? And they are usually heavy I think. But at low speeds (especially landing and taking off) they probably make a lot of difference.
Ummm.... no. You've got it exactly backwards. Winglets are most effective at reducing drag and saving fuel at cruise and over long distances. They are least effective in terms of overall efficiency at slower speeds and short distances. The 737's current blended winglet can reduce fuel burn by as much as 6% in cruise. This was recorded during the initial tests of the blended winglet on the BBJ, the first 737 to have them.
When we made the winglet an option on commercial 737s, they were at first pooh-poohed by airlines like Southwest and Alaska. Their reasoning at the time was that because most of their flights were short, and some were so short the plane spent hardly any time at higher altitude cruise, the high cost of the winglets would never be offset by the fuel savings that are at their maximum in cruise.
What happened is two things. One, the cost of fuel started to go up and still is. Two, airlines like Aloha found that the winglets significantly extended the range of the 737 because they reduced the drag at cruise and thus the fuel burn. So in the late 1990s Aloha broke new ground and started flying a couple of winglet-equipped 737s between Oakland and Honolulu. We did a video about Aloha's operation and distributed it to 737 operators around the world. And while I have no idea what role our video played, Aloha's experience broke it all loose.
More and more airlines, realizing the potential of the 737 on longer routes, began ordering their 737s with winglets or retrofitting them to their existing NextGen 737s. This allowed them to open routes with the 737 nobody had thought possible before. Alaska, one of the first naysayers, started equipping their 737s with winglets or buying them that way new and opened non-stop routes from Seattle to Washington, DC and other east coast destinations. COPA in Panama started flying what at the time was the longest 737 route in the world, LA to South America. Qantas began trans-Australia service with winglet 737s. Regional airlilne Westjet started the same kind of service in Canada. Norwegian today flies non-stop from Oslo to destinations in the Mediterranean and the Middle East like Dubai with winglet equipped 737s.
In talking to 737 operators all over the world the only comments on low-speed benefits from the winglets I have heard from pilots is that they make the plane more stable in landings in rough air.
So the big benefit of the blended winglet is at speed over long distances.
One of the reasons Southwest finally caved and started putting winglets on their planes is they want the flexibility to put any of their planes on any route. So while their shorter up-and-down routes benefit relatively little from having winglets, the ability to put the same plane on a very short route or a very long route (they are starting West Coast-Hawaii service, too) offsets in the long run the initial cost of the winglets.
One other example: I recently directed a project in China. Coming home we were booked on a Delta Airlines non-stop flight from Beijing to Seattle. We had gone over (via Tokyo) on an Airbus A330 so I assumed the plane back would also be an A330, a plane I know has the range to fly Seattle-Beijing non-stop because Hainan Airlines does it. But when we got to the gate I was amazed to see the plane was a 767. We travel business for international trips so we boarded first. When I walked on the pilot was standing in the forward galley, and I said, "Can this thing fly all the way to Seattle non-stop? I work for Boeing and I didn't think these things had that kind of range." He smiled at me and said, "Winglets." Which the plane had, a retrofit kit from Aviation Partners Boeing (APB).
So----- winglets are a cruise advantage, not a slow-speed advantage for the airlines.