A stand goes up, trades hard for a few hours and comes down. Judge any ordering system against that, not against the demonstration.
A concession stand is a small, busy shop that opens for a few hours and then stops existing. Most ordering systems are built for a restaurant that opens every day in the same room, with the same staff and a cable in the wall. A stand is the other case: it goes up on a weekday afternoon, it is worked by whoever was available, and it comes down when the last guest has gone. Judge anything you are shown against that stand, not against the demonstration.
The shape that holds up is plain. Staff ring the order in at the register and take the payment there, and a ticket prints at the station that makes it - the grill behind them, the bar next door, the kitchen that supplies three stands from the back. Guests ordering and paying from a code at the counter can sit on top of that later; the register and the printed ticket are what a stand runs on, and they are what has to be right first.
Keep the question about metal separate from the question about software. Ordinary thermal station printers speak a common standard - ESC/POS - and a system that insists on its own printer at every counter is asking you to re-cable a site to solve a problem at the till. Ask what it prints to, and whether the printer beside the register is driven from the counter itself rather than by a round trip out to the internet and back.
Then look at the signal. Venue wifi is shared with everyone standing in front of the stand and power at a temporary counter is an extension lead, so both will dip. What you want to hear is that an order taken during a dip is still taken - recorded, queued, printed when the link returns - rather than refused or lost between the two. And if the counter is worked by seasonal or volunteer hands, the register has to be learnable in the minutes before the gates open: big targets, the menu already laid out, nothing that needs its builder standing behind them.
Set two printers on a table the day before and ring real orders at them. One item for each station, then a mixed order across three stations, checking each ticket carries only its own lines under the same order number.
Then break it on purpose. Pull the paper out mid-order, finish the order, reload, and watch the missing ticket arrive on its own. Send the same order twice and confirm one ticket at each station. Unplug a station completely and see whether anybody is told. Take the stand's wifi away for a minute, ring an order, and watch where it surfaces. A system that comes through those four is one you can hand to a stand you will not be standing in.