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We can ensure that this add-on will work on the latest stable versions, which are the ones named Long Term Support (LTS). Although it may work in newer versions as well, we can't guarantee that it will work stably so if you decide to use it, save your work and use it at your own risk.
This is something you may see that happens on default objects like the Cube or Suzanne (Monkey).
Smart Weathering is meant to look good with real size 3D objects of small to medium size by default. Blender's Cube and Suzanne (Monkey) primitives are by default really big objects. The cube size is 2x2x2 meters long, which is almost as big as a room. That is why the scratches look tiny in comparison. The Fire Hydrant which is included in the test scene has dimensions close to a real one and its scale is set to 1 (this is very important as well).
We have limited it to work well with those small-medium sizes because of practicality regarding the most common objects that tend to require these types of weathering effects. In Blender, you can create something from the size of a nail to a planet, but adjusting the versatility of the tool to these extremes would cost in low practicality for the most common cases.
Keep in mind that in order to get scratches on the fillets avoid using either low poly meshes with smooth shading (and no auto-smooth enabled as well) or very organic / smooth high-poly shapes (like a sphere) as SW will not recognize sharp edges.
Also, we clarify that it is not needed to either increase the edges creases or the model is not needed to be unwrapped.
So to sum up, make sure that your object has the correct dimensions and the scale is set as "1" in every axis.