Odoo maintains a list of certified POS hardware, receipt printers, cash drawers, barcode scanners, that's known to work cleanly. Anything outside that list, a specific kitchen display system, a particular payment terminal, a scale with its own proprietary protocol, either doesn't connect at all or needs custom work to bridge it into Odoo's POS.
Running several locations raises a second issue: each register syncs its own sales back to Odoo correctly, but seeing today's performance across every location at once, in a format an owner or regional manager actually wants, often means pulling data from Odoo and rebuilding that view separately rather than Odoo producing it on its own.