There are no long term contracts or commitments on your part. You simply pay month-to-month. You can cancel any time, and you won't be billed again.
We have a one-time campaign that you can purchase if you do not want a recurring monthly campaign. Monthly campaigns have several benefits including that you will have 20% more impressions for the same amount you paid.
You will have a normal and healthy growth pattern without any suspicious spike.
If you want to cancel your subscription though, you can do so from your Featured User report page.