Really cool extension! Another advantage over Anki that I could identify is being web based. I see the potential of Supermind making learning a collaborative experience through sharing cards and other learning resources.
You can, and I've done it some since migrating to iOS until I feel like I'll use it enough to pay for the app (I suck at sticking with flashcards; they're so boring).
The collaborative idea is something I'm thinking about. I want it to eventually balance on "easy sharing / collab on sets of cards" with "still able to be personal", since learning is fundamentally a personal experience. I'm happy to talk about this more or setup some time to talk: please email at arh.hoskins@gmail.com
It also features a database of user-contributed decks[1] on various topics.
That said, I don’t know whether AnkiWeb could be used completely without the accompanying desktop or mobile app.
[0] https://ankiweb.net/
[1] https://ankiweb.net/shared/decks/