Does anyone know what the difference is in using the trial version?
Knowledge says
Note: The trial version of Form Builder is not feature restricted.
If there are no feature differences what is the gain in moving to the "non" trial version?
Form Builder has traditionally been a paid feature. However, it may be included at no cost to your organization. The app store does not know what agreements you have in place, so it will always say trial when looking it at in the app store. I would talk to your CSM to see if it is a paid feature or not for you.