The upturned wingtips have the aerodynamic quality of extending the wing span, making the wing more efficient due to the higher aspect ratio, without making the wing longer, which could cause parking problems at some airports.
The upturned tips are most effective at a single cruising speed, which has been determined to be the most efficient for the plane.
For models, which don't cruise for any extended periods, these tips create drag throughout the flight regime.
For long duration models which will fly at a single speed, these "winglets" can be useful.
Some 3D manuvering planes add them for the side area useful in knife edge and other wings vertical flight.
Following Tony Frackowiak's modifications to his full-bodied Tribute, I added verticals to my long-suffering profile Tribute.
The flight characteristics have changed a lot, and it will take some time for me to finger out what's going on.