Open Bitcoin ATM transacts Bitcoin with pre-rendered QR codes stored locally on the machine. While there are tradeoffs, this approach has four important advantages:
1) Significantly reduces cost and complexity of ATM platform.
2) Eliminates security, performance, latency, and uptime risks associated with network connection.
3) Makes transactions very fast and convenient (no need to access blockchain with every transaction).
4) Allows for ATM operator to mitigate risk of Bitcoin currency fluctuation.
5) Mitigates risk of loss due to theft.
While the QR codes are pre-rendered and stored on the ATM, the BTC value is not. This means the wallet value can be updated anytime before the QR code is dispensed.
For further precision and control, QR code inventory may be time boxed (future dates and times) and the BTC value assigned according to the spot rate just prior to the time box. This is a convenient way to mitigate exchange rate risk.