they are not a susbstitue for lower wing loading that is they can NOT increase lift

But they will change lift to drag relationships ( very important) and the right one for your needs will take some careful experimenting.. some pattern guys use the flapperon feature to trim a model that is the EFFECTIVE airfoil shape can be tailored to setup a different wing to fuselage (the thing some call the main wing as opposed to the little wing on th e back of the body) relationship. the relative , effective AOA
The model will then fly tail high -or low- depending on the trim of the flapperon.
It's fun to futz with but the practical aspects of it are kinda iffy.
do your tests gently -a little at a time - like kissing a duck -it takes practice.