title: Adding the billing card to the Heroku account and cons/pros of using dynos
body: <p>Since I am not very familiar with Heroku I need opinion of a specialists like you. I got two questions to which I cannot find an answers on the web.</p>
  
  <ol>
  <li>Heroku tempts with the 450 dynos if I add the billing card.
  <strong>Is that secure to add it?</strong> </li>
  <li>Will they take the money from my account without my permission? If for instance I have used all the dynos, would they take the money from my account to add some dynos?</li>
  <li>Do dynos last for long? How many users can use my site if I got 1000 dynos?
  I tried to understand the answers from the another questions here in stack, but I could not understand them.</li>
  </ol>
  
  <p><strong>Please do not use the technical language, try to answer these questions as simply as you can (for me and users who will read it).</strong></p>