LLN is good but seems to favor anti-features like disabling text selection on subtitles (except in the side pane) in order to push their in-house paid-for features.
Regarding your comment about extensibility, this applies to mostly every software platform other than the web, unfortunately. And even there, it feels like a happy accident. There's much work to be done in this area.
Text selection is a fiddly CSS issue that Ognjen didn't get around to fixing yet. There's only two paid features (saving words and machine translation.) About 3500 paying users at $3.50/mo after taxes and fees (from 800k total users), but before paying for servers/APIs, if you are curious. Free users are welcome.
[ Dear Netflix, let's be friends. There's a lot of work to do still, and we can go further, faster, with some small helps. Can we get a test account? Regards, David. languagelearningextension@gmail.com ]
Regarding your comment about extensibility, this applies to mostly every software platform other than the web, unfortunately. And even there, it feels like a happy accident. There's much work to be done in this area.