Here's a question; why aren't these more commonly used? It seems like it would be easier to attach a tip on the end of a wing as opposed to cutting a section out of an existing wing? At the very least it doesn't seem like there's a very large disadvantage (except maybe control linking and structural strains at the rotational joints) to having the wingtips act as ailerons/elevators?
As an example;
Westland-Hill Pterodactyl Mk. IA