Your scepticism is understandable - and for some computing platforms your observation may have substance. However, this is not the case in context of recommendations to utilise 1Blocker with Apple platforms. Some understanding of the App, its implementation and associated Apple processes might help you to understand why...
All installable Apps receive the same level of vetting, by Apple, before being approved for distribution via the Apple App Store. Vetting doesn’t end in a one-time process; code review is an ongoing process.
Likewise, external/third-party blocking-services that are dependent upon a connection, by your device, to a third-party proxy may be dubious - as you have no control over the routing, processing and/or potential skimming of your network traffic. By contrast, 1Blocker rule processing is entirely within Safari itself via the native Safari blocking API. 1Blocker simply builds the filtering rule-set used on-device by the Safari Browser; 1Blocker has no knowledge and zero visibility of your actual network traffic. Note also that 1Blocker is available for both iPadOS/iOS and MacOS.
You should be reassured that, due to the restrictive sandbox architecture utilised within iPadOS/iOS where few anti-malware defences are exposed or available, this is a valid and effective measure in reducing your exposure to browser-based exploits. The suggestion to utilise 1Blocker is sound option - and is used by many IS Professionals in reducing threat exposure. It always remains your choice to follow any security recommendation - or perhaps not according to your [hopefully qualified] assessment of relative risk.
Other techniques are also available to protect all network traffic - extending the browser-based threat mitigation that I suggested. This a more advanced topic beyond the immediate scope of this discussion thread.
I hope readers will find this clarification to be helpful - in context of using a reputable content blocker product - and in understanding the safety of the proposed mitigation strategy and the broader threat.
