The main purpose of 1Blocker's in-app filter is to protect your privacy against in-app tracking.

While it may prevent some ads from loading along the way, not all of them can be blocked using this approach due to the technical limitations of iOS. For example, YouTube and Instagram in-app ads are impossible to block even with the in-app blocking tool enabled.

It can occasionally block some ads, mainly if they rely on trackers.

Since targeting specific in-app ads is currently impossible, ad-blocking inside apps is a nice yet sporadic addition to 1Blocker, while its principal goal is to prevent in-app trackers from collecting your personal information.