Free fighting is generally an event, not a fighting system. It can be understood that there is generally no boxing leg or elbow or knee throwing method in the rules.
Sanda is three techniques of wrestling with fists and legs.
Relatively speaking, Sanda is a project created by China people, so his theory, system, personnel and coach are relatively easy to find.
Fighting is a practical operation, and depending on the level of coaches you like and meet, it will have an impact on your actual combat effect.