Alll wysiwyg barcode apps give you many opportunities to produce barcodes that are substandard, difficult to read, perhaps unreadable or even be misread. Most clients use barcode in supply chains and are obligated by contract to attain minimum industry standards. Sending out bad barcodes can be very expensive. Chargebacks and loss of customers are common.
The only way to insure you are producing acceptable codes is a testing method called ANSI/ISO barcode verification. This method grades barcodes quality and their ability to be read by the variety of scanners in use. Simply scanning a barcode with your scanner proves nothing other than your scanner can read it, not that it is a good code or that other scanners should be able to read it as well.
Using ZPL and commanding the printer directly is not a guarantee for quality either. There is a somewhat lower chance of error but it is still there.
You are shooting in the dark without verification.