Cheers. I noticed that you, the developers of this application use GPL v2 libraries, and linking against them. The thing is that linking a GPLv2 library in your closed source application, it will become a derivative work according to the clause 0 of the GPL v2 License. So, that means that this application should be licensed under GPL v2. That also means you need to have a way to give the source code when requested (to others, there is no problem selling software with GPL v2 license, except it's open source.
So, who may i contact to obtain the source code?
Even if you disregard my comment, you should at least comply to the most easy parts of the licenses used here; to give Credits to the copyright holders, that most of the libraries used demands according to the licenses.
To give one example. You use older versions of libpoppler, that goes under GPL v2. As it states in the README file, that are not present in your build:
”Please note that xpdf, and thus poppler, is licensed under the GPL,
not the LGPL. Consequently, any application using poppler must also
be licensed under the GPL.” .
Also, you claim this is 5x faster than other eBook converters, which i find very hard to believe, as the underpinnings is almost the same as Calibre, alas reorganized and boosts less features. An as it seems, there are plenty of apps clones and look almost the same as this, both on Windows and Mac and do the same stuff. Also, the webpages for the products, including yours almost always is built the same way, uses the exact same ”selling texts”. But more interesting, most webpages (including yours) also have a link page with links to ”friends” or ”recommended software” that for some reason always include Wondershare.
As your software and the identical clones uses the exact same strategy as the applications by Wondershare that goes under different brands and names, you may not be surprised that i believe that you may belong to this category. The company on your page, that holds the ”copyright”, don't even exist.
But it gives a feeling that it's based in Europe or Japan. However, the traffic from the site mostly comes from a large Chinese Social Media site (think Facebook), and somehow, the ones ”reviewing” this app, and some of the Wondershare ones (including the Wondershare owned clone Brands iSkySoft and so on), seems to be the same persons. On some occasions, they reviewed or gave tips on other software, but always with a ”but these are slower or not as good as product X”. This is a pattern you see on english based sites and forums also.
It's not that hard to see which of the users that are fake ones. Somehow cute when you see the use of Shutterstock photos added to the ”profile” of the raving reviews.
And the fact that you, the ones that made this app and others, hide who owns the domain via the GoDaddy service Domainbyproxy don't really feel like a good thing to do, as it feels like you are hiding something.