Will I be locked into buying proprietary tape or labels?

Sometimes. r/printers notes some mini label makers use RFID-chipped cartridges that refuse third-party refills. Brother TZe and DYMO D1 cassettes have cheaper third-party equivalents, though community members warn the adhesive on generic tape can be weaker. Thermal shipping printers are generally the most flexible, accepting most standard 4x6 direct-thermal label stock.