Actually, the stall fence, the winglet, hoerner wing tips etc all do the same thing. All wings lift because of the higher pressure below. At the wing tip the air leaks over from lower to upper side. This forms a wake vortex which adds drag. Further, as the wing goes through the air, it displaces air. Air wanting to take the path of least resistance, flows along the tapered leading edge instead of over the wing (this is called washoff I believe, havent read up on aerodynamics in several years). All of these make the wing less effective at the tips.

All those who fly passenger aieplanes have seen the winglets at the tips. In Boeing these are curved upward whereas Airbus prefers T-tips. If you see eagles or ducks in flight, you will see the outermost feathers curved upward. They all have the same function. These winglets prevent the air from leaking over and force the air to go over the wing. This has two effects- it makes the wing more effective in contributing to lift by zoning the air pressures and it reduces wing rock- wing rock is caused by one wing tip stalling then the other. Yes, the wing tips also add drag- I believe its called lift induced drag or it is a component of lift induced drag. But it makes flight more stable. The same principle is employed in F1 wings- you see all the nose and tail wings have end plates that serve this purpose. In addition to reducing wash-off, they make flight more efficient by reducing energy loss in eddys at the wing tips

In our hobby, SFGs serve the same purpose. Large ones add more rudder authority by making the rudder contribute more towards steering rather than stabilizing the airplane.

Winglets wont add too much height- I dont intend to make them too large, just an inch above and below the wing and restricted to the fixed part of the wing only. I feel its a good idea

With respect to losing weight, I already have 3.25" foam wheels installed. I retained the stock LG instead of the CF LG (80g addition) and used 4 cell NiMH insted of LiFe (40g) addition. There is not much else I can lose to save weight. I didnt install the cowl (though I test fitted it) as the engine is still in break-in and I didnt install the spinner as it will just make it more nose heavy (its already 15mm front of the recommended CG). Both save weight, not a bad idea to keep them off

Ameyam