Any device below should work for a popup. The Shopify POS app works with devices that meet the following requirements:
|iPhone||iPhone 5s or better running iOS 12.2 or higher|
|iPad Air||Generation 2 or better running iOS 12.2 or higher|
|iPad||Generation 5 or better running iOS 12.2 or higher|
|iPad mini||Generation 2 or higher running iOS 12.2 or higher|
|iPad Pro||All iPad Pro models running iOS 12.2 or higher|
The newer and/or larger the iPad (storage wise) will determine how quickly the POS app is able to load larger inventories. However; outside of larger inventories, you shouldn't see any issues when using any of the above devices. More information on the Shopify POS can be found here.
Let me know if you have any questions.