It seems like it can tick many of the boxes for effective long term learning if used properly (including not just surface learning but also deep conceptual understanding). However, my impression is that there is a learning curve and a cost associated to using it consistently, which leads to it not being used as much. Idk. What’s your experience?
To the other great responses here, I want to add that the act of creating cards for your deck, especially when you go beyond a straightforward multiple choice format, is in itself a form of study. To create a good test question usually you are digesting the information more deeply