As of March 2024 this addon appears to be abandoned. Do no buy it unless you are using an older version of Blender (up to 2.93) and you accept that you will probably not get any support.
Here is a GitHub repository that seems to have been updated more recently than the Blender Market product (I don’t know if it contains anything useful): https://github.com/jamesvsnowden/bl_rbf_drivers