They are the same plan. Hesiod is licensed under GPL-3.0 — free to use, free to study, free to modify, free to pass on. The columns exist because pricing pages have columns.
What makes Professional most popular?
The border.
Is there a trial?
The trial is the software. It does not end.
Can I talk to sales?
There is no sales team. There is a Discord, and there is an issue tracker, and both are better company.
So how do I pay for this?
You do not. If you want to give something back, report a bug you have reproduced, improve the documentation, or send a pull request. Terrain you are proud of is also accepted.