From a marketing aspect the word "free" carries negativity with it. For most companies the cost of one software license is negligent and easily overcome by the marketing of the larger suppliers such as Rockwell and Wonderware.
Its easy to take the strengths of AdvancedHMI and use it as a weakness against the other HMI's. Have you ever had to completely redo a system because the hardware it was based on became obsolete? If the panel PC that AdvancedHMI runs on goes obsolete, then just buy another brand. Try that with Rockwell. The Wonderware fans will claim they do the same thing because it is PC based also. How long will it take to transfer and activate the licenses? Have you ever had one of those licenses decide to deactivate and halt the system?
What about the time a PanelView goes out and a spare is no where to be found. Can you run to Wal-Mart? With AdvancedHMI you can run to Wal-Mart get a laptop to temporarily stand in place of the Panel PC and have the system running again in a short time.
So then there is the flexibility. Let's say you create a production display. Then comes a manager who wants it running on his desktop. Buy another license? Or just copy the application onto the PC and have it done the same day.
So my advice is to stay away from selling "free". Sell capability, flexibility, long term cost, and potential downtime savings.
Here are some other things to think about:
https://blog.advancedhmi.com/index.php/2017/04/12/top-10-reasons-advancedhmi-is-a-better-choice/