I should also consider if there are any limitations on the number of devices, sensors, or the ability to monitor certain types of networks. For example, the free edition might be limited to 10 core (physical or virtual) devices. Each core device can be scanned with all possible sensors, but adding another core requires a commercial license.

Another point: the free edition might not include technical support, which is a consideration for businesses that need help. Emphasize that for critical infrastructure or larger networks, the commercial edition is more appropriate.

I should also address what exactly constitutes a "license key" in the context of PRTG. Most software requires a license key for installation and activation. Maybe the free edition doesn't require purchasing, so the "license key" is generated automatically upon download? Or perhaps Paessler provides a license key for the free edition through their website. Maybe the user is under the impression that there's a special license key that grants exclusive access to the free version. That might not be accurate, but I should explain it properly.