I've been using GC since at least 2000, maybe earlier, honestly can't remember. Developer has DEMONSTRATED over a long period of time a consistent track record of improvement, speedy bug fixing and functional enhancement. And isn't that what we all want in any app and developer? For us old timers, that's what we used to call 'support', a term many current apps and developers have forgotten or ignore.
In any app as sophisticated as GC with as many features, it is always a challenge to implement a UI that balances ease of use with power; that is a challenge not unique to GC. If you haven't tried GC, do so. The app is still provided as a fully functional shareware app; how many apps can you say that about anymore?
I know there are folks who tout Pixelmator, and that's fine, I'm not dissing Pixelmator. I tried it. For me personally, I can't get past the tiny, white on grey UI of Pixelmator, perhaps younger people with younger eyes can handle, perhaps it's just my old eyes. It is kind of ironic to read comments about GC's UI being antiquated; when I find PIxelmator's UI almost physically unusable.
If you already use GC, then I'm preaching to the choir, if you haven't tried it yet, give it go.
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.