What is the meta-point — how does this app apply spaced repetition and the testing effect?

This very app schedules your cards with exactly this FSRS logic — showing each card right as you're about to forget it.

Every flashcard and duel you answer feeds a per-card memory estimate; the scheduler then surfaces each item near the moment its recall probability dips toward the target. That's the most efficient possible use of review time: no wasted reviews on cards you'd ace, no forgotten cards left too long.

So the cards teaching you the algorithm are themselves being scheduled by it — learning how to learn and watching the machinery run, at the same time.