Exactly, this
free package only allows 25 responses/month.
So it is thought to have a first glance at the application, test a little bit, and then register for one of the other packages.
Here you pay for the convenience of not having to worry about hosting, nor about updates, nor about backups.
And you should read about the counting of responses in the FAQs at the bottom of this page.
How are responses counted?
In short...
A response is counted if a participant completes your survey once, regardless of how many questions or question groups your survey contains.
In a more detailed description...
A survey is taken and completed => 1 response
A survey is taken and only half completed => 0.5 response
A dataset is manually added by an administrator => 1 response
A partially completed survey is marked as finished by an administrator => 0.5 response
The CE version is free of charge.
If you choose this one (it does not differ from the pro version), you have to take care of all this yourself.
Or in other words: Youhave the freedom to do everything yourself.
Joffm
But in general:
This forum supports the CE edition.
For the Professional edition you may ask LimeSurvey GmbH directly "Support / Contact us".