For those users classified as "beta testers" (at this point all users are so classified), the usual pricing scheme is modified.

You will not be billed for any money, even after you have completed each unit. In place of money, we ask you for feedback. As you work through your exercises, the system will occasionally query you about your experiences with LanguageDoctor.com.

Brief answers are fine, but to continue receiving free service you must provide information when requested. You do not have to remember to initiate any feedback (although of course you can still do so if you wish); the Exercises page will prompt you when appropriate.