The review you mentioned likely discusses the effectiveness and legitimacy of a specific tool or service claiming to offer private Facebook profile picture viewing. When evaluating such reviews, consider:
The short answer is that there is no legitimate "online viewer" tool that can bypass Facebook’s privacy settings to view a private profile picture or a locked profile facebook private profile picture viewer online
The concept of a "Facebook private profile picture viewer online" The review you mentioned likely discusses the effectiveness
If you're looking for alternative ways to view Facebook profile pictures, consider the following: facebook private profile picture viewer online
: For legal parental control purposes, software like mSpy or uMobix can see activity by monitoring the device itself rather than trying to hack Facebook's servers. How to Protect Your Own Profile Picture