Anki is definitely incredible! But it's in no way easy to use once you do anything more than a few hundred simple cards.
Just take a look at this video, and the apps ui, and tell me this isn't a clusterfuck: https://www.youtube.com/watch?v=2Y35WiKNbCU
So yeah, for a simple flashcard app, it might be easy to use, but if that's all you need there're better tools.
As for it being free.... Yes, and that bothers me. I would rather pay $$$ for a great product than use an okay one for free.