The module is developed by @maaakstiles and I really like it because it’s easy to extend/change to fit your requirements. The basic idea is very easy. It gets data from somewhere (Sitecore/CSV/SQL/MySQL). I played with the SQL part.
I would like to import files from another database and create a media item from it. To make it work I had to do 2 changes.
Make it to deal with byte
So now I have the byte array converted to string. This value is passed to the FillField method so now I need to change that to attach this stream to the media item.
Remaining step is create a new template for Field in Sitecore and use it. This video shows how you can do that: