A split flap acts as more of a brake. I have them on the full scale I fly and you get a pretty good pitch up when you use them. You will want to hold down elevator when you deploy them.

They don't change the upper airfoil. Look at some of the old TBM type birds. They had split flaps, but had holes in the flap itself. That makes it even more effective than being solid. The designer wanted me to make holes in the landing brake on my full scale Long EZ to make it more effective, but I didn't want to have to re-design it for the holes and have to re-do it to make it stronger. It would have been a better design.