While I can't speak for Mochi Cards, if you're looking for a spaced repetition app that allows sharing, I'd recommend my own [1]. Sharing with friends and teachers is built into the app.

If you're particularly interested in pre-made sets, both my app and Mochi Cards rely on importing from Anki and Quizlet, which both have a large amount of pre-made sets.

[1] https://get21stnight.com/

Sharing isn't built into the app yet, but you can export decks and share them.