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I feel this is easier than those solutions in a lot of cases - mainly because you don't need to install anything. Just open website, drag and drop a file, pick target format, done.

Which is only true if you are not interested in the “self-hostable” part and you installing an app is a significant difficulty.

Once an app is installed locally it is more convenient to use - that is why it is so common for apps to replicate (or just wrap) websites.

If you are not interested in the self-hostable part there are lots of online converters.

Right, but those online ones are also usually covered in ads, don't run locally, and run the risk of infecting the output with malware.

It's not clear to me why that's a problem?

It's a web service that can be used on any device without installation. Think in terms of usability for old, non-technical folks.