I don't think there would be any change in the control effectiveness, as long as the gap is tight; the relationship between the leading and trailing edges is the same as a "normal" installation.

There would likely be a little extra drag from the little low-pressure area in the gap. On a full-scale plane this can add up to a knot or two; my plane has little 2" gap-sealers on the flaps that make a small difference when they are missing. It's probably negligible unless you are pylon racing or something.

Just armchair aerodynamics, FWIW.