Portable, mobile, and the difference that matters
Portable generally means it leaves the counter but stays on your premises — table service, a beer garden, a showroom floor. It leans on your own Wi-Fi or a Bluetooth base, so it is only as reliable as the network it sits on.
Mobile means it leaves the building. That needs its own 4G connection, which is a running cost but removes the dependency on someone else's Wi-Fi.
The failure we see most often is a portable device bought for a mobile job. It works in the showroom and drops out in the driveway.
What to check
Battery life against your actual shift, not the spec sheet. A device that lasts a lunch service and not a full trading day needs a second battery or a charging base, and that is a cost nobody quotes upfront.
Whether the 4G data is included or billed separately, and what happens to a transaction when the signal drops mid-payment.
If you take tips or split bills, test those specifically. They are handled differently device to device and it is not something you want to discover on a Friday night.
What it costs against a countertop
Portable and mobile devices usually carry a higher rental than a countertop, and where merchants lose money is buying one per staff member when the trading pattern only ever needs two.
Worth sizing against how many payments are genuinely taken at the same moment, rather than how many people are on shift.