Key Difference between Mobile and Countertop:
Connection Interface: Countertop build in Ethernet and 3G, Portable use 3G and WiFi.
Price Difference: $10 more on monthly cost for mobile.
Countertop: Good for shop that check out at counter or self check out. Connected with Lan, which is fast and stable.
Mobile: Good for shop that checkout at table and need to move the EFTPOS everywhere like casual restaurant and bars.
For countertop, you need an additional LAN socket at counter and power socket for it.
For Mobile, you just need a charger somewhere in you shop.