There are two main types of extrusion, Radiused Korner Light (RKL type) and Radiused Korner Full (RKF type). Choosing the type of extrusion is based on how you plan to use the extrusion for your design. The first thing to consider is do you need a “full” version of Kangaroo Extrusion.
Full style extrusion (RKF type) offers several benefits. The first is 3 holes running through the length of the extrusion. It is also thicker with a larger cross section of a material making it more stiff relative to the light version. Multiple holes allows you to use multiple screws when connecting the extrusion to the top and/or bottom panel. Another reason to use a full extrusion is you want to attach something where the first hole (concentric to the radius) is, such as a rubber foot, and can then use the other 2 holes for attaching the base to the extrusion. Thirdly, if you want the extrusion to be more rigid / sturdy then using the full extrusion makes sense as it is more robust / sturdy than the light style extrusion based on overall cross section for the same size.
If none of the above apply (multiple screws, attachment options, more sturdy) then the light style extrusion may be a better choice for your application.