You only need to pay for the experiments where you want to analyse more than 20 responses. You can collect any number of responses without paying first, and only pay when you are ready to see the reports. Generally, experiments with 20 respondents or fewer are useful for testing the tool, but typically cannot provide reliable results.
If you want to test with ~50 survey testers, you can use our Quick Feedback functionality.
This question from our users was answered on 20 September 2019. If there is anything else you'd like to know, please do not hesitate to contact us.