RAM and storage
4GB RAM is the minimum we would consider; 8GB feels smoother. 64GB storage is fine, 128GB gives breathing room.
Android version and chipset
Newer Android versions support more apps. Chipset names such as Qualcomm or Snapdragon usually signal better performance than unnamed chips, but check reviews.
SIM or no SIM
A SIM slot gives the box its own data. Without it, use Wi-Fi or a phone hotspot. See the 4G SIM boxes.
Seller and returns
Check ratings, order counts, recent photo reviews and the return window.