Safari has this feature built in as well. It is particularly useful on mobile devices. It will even follow Next Page type links to condense a multi-page article

Safari has this feature built in as well. It is particularly useful on mobile devices. It will even follow Next Page type links to condense a multi-page article into a single scrolling page. I find it somewhat ironic that Reader Mode's own site is filled with large images, tiny pop-out boxes, and a tweet carousel. But it certainly isn't the worst product website I have seen.