The FBI's sales pitch to alleged criminals was that these were security-focused devices (so please use them to document your illegal activities!), and that involved a lot of fun security theater. A "pin scrambling" feature would swap around the order of the lock screen numbers so that no one could guess your code from screen smudges.
Two different interfaces would launch depending on what PIN you typed in on the lock screen. PIN one would show a bunch of popular but non-functional apps, like Tinder, Instagram, Facebook, Netflix, and Candy Crush. Presumably, this was meant to fool any third parties checking out your phone.
A second PIN would enter what was supposed to be the secure section of the phone, showing three apps: a clock, calculator, and the settings. From here, the "calculator" app actually opened a login screen to Anom, which targets were told was a secure, encrypted way to chat. This was basically the smartphone equivalent of a fake book triggering a bookshelf to slide over, revealing a secret passage. It's so secret, it has to be secure!