Guardian is able to protect against 90% of page hijackers that will cover a webpage in this manner. While we are not specifically an "ad-blocker" app, we do block aggressive ads that cover webpages as you browse on your device. Many of these page-hijackers are maliciously attempting to cause a user to enter information or tap on their banner in order to direct the user away from the webpage you intended to visit.
If you notice an ad that covers the entirety of the webpage that is not effectively blocked by Guardian while using Guardian, we encourage you to take a screenshot of the ad and email the information to us at support@guardianapp.com so that we are able to review and improve our blocking capabilities.