KF by the way stands for Kline and Foggleman, the engineers designed the basic idea.
A KFm airfoil is easy to obtain in any material – from cardboard to laminated foam sheets, in order to make a layered, stepped profile. In the aeromodelling groups, they are widely used and there are long threads for both general building and scientific discussions.
There are KF profile variations, from positioning the sheets to obtain a profile that emulates traditional (curved) airfoil profile.
The percentage thickness refers to each sections total thickness compared to the total chord of the airfoil, and not the height of the step which is only determined by the thickness of cardboard or foam sheet. Steps can be raised to give more height and the step effect increases proportionally with both height and air speed
The most used sections being KFm2, KFm3 and KFm4, because they are the quickest and easiest to make, still flying well.
Many of designs that use a KF airfoil have similar flight characteristics. Flying wings especially benefit from the additional control authority caused by the more adhered airflow over the control surfaces.
The KFm profile airfoil has an acclaimed performance in the introduction to aviation via aeromodels, because it is easy to obtain and easy to be used to explain the aerodynamics.