The extension allows to save a Wikipedia article to the default reading list.

But that's it, it doesn't implement any other reading list feature - a particular reading list to save the article into cannot be selected, it's not possible to remove the article from a reading list, reading lists cannot be managed or even viewed, so it's actually a "write-only" feature - you can save articles, but you cannot view them, so it's close to useless.

I'm using the reading lists to save articles I'm interested in while on a mobile phone to read and research them later while on a desktop computer. But there's unfortunately no way to access those reading lists on a desktop.