Price history and alerts
Free shows the last known price. Pro keeps the full history and notifies you when a card crosses a threshold.
Every card keeps its last known price in the free tier. Zukan Pro keeps the full price history of every card, so you can see when a card moved and by how much.
Pro also adds price alerts. On a watched card, tap Set an alert, enter a threshold in your currency, and save. When the card crosses it, the app sends a notification on the phone. The first time you save an alert, Zukan asks permission to send notifications; if you refused, turn them on in your phone's settings.