The most effective aileron's are sealed Aileron's! Tip plates can control lateral movement of the wing as does a rudder. Tip plates are not creating dirty air across a control surface so they have no viable use other than a stabilizer ie. Rudder.

A 100% totally clean wing will have lousy control capabilities at various speeds. Thats why Aircraft have what is called a Vortex Generator. What this?(It's a bunch of little piece's of metal sticking up in different directions to dirty the air prior to it getting to the control surface.) Dirty Air.

Say you purchase an ARF or build any of the funfly style aircraft, of any performance nature with Flat wing tips. You take it to the field and it just won't stay put on knife edge. Always wants to fall out, your always fiddling with the ailerons trying to maintain a crisp knife edge. You now put some winglets on it and it holds steady. Why? Because you've created two more rudder surfaces.
Now you take that same aircraft and buy some clear Ultra-coat if you have an Arf. And you seal the Whole length of the Aileron's and the Elevator. Your Airflow across these surfaces no longer have the gapppppppping Hole/slots and I'll gaurntee(Texas Draw LOL) you that your aircraft will have a new personality. More responsive as well as CA Hinges are now double protected. Chances of High speed flutter has reduced 50 %. Hope this makes a little sense. If not I'll be a little more eliquent/literary on the next response.

Anti-Stall Wingtips: They work better with low speed aircraft and Clark Y Airfoils. Reason behind them is a Clark Y is a Flat Bottom wing it's always creating lift as long as the Aircraft is in motion. The 45 deg under cut Tips(Typically called Anti-Stall tips in the hobby) have a self righting tendancy. In other words if you let go of you controls on a bank cut the throttle back and the plane will try to right it self.