Any device below should work for a popup. The Shopify POS app works with devices that meet the following requirements:
iPhone 5s or better running iOS 12.2 or higher
Generation 2 or better running iOS 12.2 or higher
Generation 5 or better running iOS 12.2 or higher
Generation 2 or higher running iOS 12.2 or higher
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.
Trevor | Community Moderator @ Shopify - Was my reply helpful? Click Like to let me know! - Was your question answered? Mark it as an Accepted Solution - To learn more visit the Shopify Help Center or the Shopify Blog