Appears to work as advertised. Installed the add-on while already logged in to Wikipedia, and the add-on detected that I was logged in and worked immediately. Note that you have to have reading list syncing already enabled on your mobile device.

One downside is that you can only save to your general reading list (called "Saved" on mobile and "Saved pages" on desktop browser), not any of the named/themed lists that you can create in the mobile app. You also cannot read FROM that list via this plugin, only save TO it. If you want to read from your list, you have to find it on your profile page at the Meta Wikimedia website, under "Special:ReadingLists/"

Handy for the sake of just adding something to my saved articles, but I wish I actually had access to my saved lists on desktop, both for saving articles and pulling them back up. At least it does what it says it does on the tin.

Would love the addon because the idea is great. But it doesn't even show up. :(

EDIT: its in the address bar lmao
You should make it a bit easier to see visually.

Sehr praktisch, aber ausbaufähig!

Only allows syncing to reading lists, not viewing them. To do that, you need to use the app. Wikimedia really needs to implement a proper article saving feature that works across both the app and the web versions of Wikipedia.