We believe that you should retain your customers because your product is better than the competition. Not because you impose some sort of data lock-in.
You can easily take your notes out of Collected Notes, just go to your profile: https://collectednotes.com/accounts/me
And click on the button that says: “Send me a .zip file with of all my notes.”.
Shortly after doing that you‘ll receive an email with all your notes attached as Markdown. Super easy.