I just took one of the surface files, right clicked on the the surface in the feature manager clicked diagnose and got a solid...it did not work for all the files I'm dealing with...
I was wondering the same thing...
I have some STL files that are only 1.2 MB or so and the STL importer that comes with SW can't generate a solid (only a surface)
I saw the add-in you are talking about (created in 2002???)but want to make sure it works before I buy it ($200)...