Compare a Spaced Repetition App Against Paper Flashcards for Vocabulary

The app promises science; the index cards promise you will actually use them on the bus. This compares the two on cost, how well each fits a real routine, and what the research on spaced repetition actually supports, then picks one for a set weekly word target.

Compare using a spaced repetition app against paper flashcards for building vocabulary in {SUBJECT_OR_LANGUAGE}, covering: cost and setup time, how well each fits a phone-in-pocket routine versus a desk routine, the retention evidence behind spaced repetition scheduling, and the one scenario where paper wins outright. Give a clear recommendation for someone learning [50] new words a week, not a balanced non-answer.