Hi Evjl's Rain,
Both products have the same protection and detection features. Free has a minimum update interval of 2 hours compared to 15 min for Pro. The paid version has also more configuration options, e.g. for the real-time scanner. No technical support over phone and email for the Free version.
There can be different reasons why the testing results varied. It depends from the testing scenario and product version. Example: If the unknown files have been uploaded once, they will not be uploaded again and just compared with the file hash for a decission.