I did a big surge of learning this way for a post-graduate exam in 2010. It was very effective, much better than any of the 'usual' ways of learning.

However, once the exam was over, there was no way I could maintain the 1 hour plus of card review each day. Eight years later I remember very little of what I learned.

Admittedly I was studying quite hard, ending up with nearly 4000 cards after 6 weeks, perhaps there is more luck with less intense schedules. The material was also complex and esoteric.