First off, I am aware this tool is around for several years and has many great features. The big problem is that GraphicConverter stood still in time regarding the user interface. In fact, it is terrible looking and worse, it is not very intuitive at all. The features are wide spread in a maze of menus, buttons and dragging.
Maybe it works for users who are familiar with it for a long time but for newcomers it clearly is not. In short, the learning curve is terrible steep, even for doing simple things like scaling a bunch of images. I really urge Lemka Software to take a look at modern macOS interfaces and see if a rework is doable.
Conclusion: GraphicCOnverter is mixed bag of good features packed into an awful working and looking UI. I don't like it at all.