Hi,
you will correctly need a feature license for your QFX switch - but as you can see it will work. Just every time you commit it will result in an error telling you that a license is missing.
This makes it easy to test things but to continue using the feature, you must buy the right license to be honour the license agreement.
If you can provide the exact name of the QFX switch, I can provide the right SKU - if you are in doubt about this :-)
If the switches are in a virtual chassis / virtual chassis fabric, licenses are only needed for the RE and backup-RE.