So far my experience with mobile security apps is that they end up slowing down your mobile phone like a lot and randomly end up installing other apps that you did not want to.
In mi opinion a mobile phone is not in the need of external security apps duo to the integrity and own security of the apps by themselves, all the apps that you may be using such are whatsapp, facebook, gmail, etc (not only the well known ones) have already enough security integration with scripts, encriptation and many more things in order to avoid any kind of data leak.
Of course I agree that any extra app which works in background will impact your phone speed. Maybe you don't see positive influence because nothing bad happened to your phone and data?
I was just curious because there is a lot of articles like: https://www.netguru.co/blog/ios-app-security-how-to-protect-users-sensitive-data-in-mobile-applicati... - guides how to protect your phone and if it is not helpful who use it?
I agree that external apps, especially this very popular such as FB, gmail etc. are enough protected. But how about your gallery or messages?