It's the perfect addon for making nice epubs out of those websites.
It's actively developed (and improved), and the devs actually care about user feedback.
Well done.

One of the most recent features added was Wayback Machine support. So you can grab archives of novels even after the sites this extension supports are non-existent.

This extension is very easy to use. Just navigate to a volume on a supported site and click the icon for the epub generator then just Edit any of the fields you want to change and click "Pack Epub".