you go to the table of content, select which chapter/volume to download, click, and save. well, it doesn't work on Baka-Tsuki, but it works for most of wordpress sites. it also works on RoyalRoadLegends. well, normally I would rate this 4/5, but because it's the only one with a really tidy epub, I rate this 5/5

I can't find use it on mobile

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".