It's very interesting observing people use the app in person, as opposed to privately on their phone where you have no idea how they interact with it.
For instance the Stripe Terminal reader is immediately to the right of the iPad POS, but a good number of people don't know where to tap the card. I need to design an arrow on the checkout screen for that because I've seen many people tapping the card to the iPad screen. I think Square got them used to that.
