Aegis: 2fa. Free, open source.
Auto Auto-rotate: per app rotation settings. Free, open source.
Missed notifications reminder: adds a repeating sound or vibration if a watched app has an active notification. Ie, you got an email when you were away from your phone so every few minutes your phone makes a beep or whatever so you don't need to check the screen constantly. Free, open source.
MJ PDF: simple, fast PDF reader. Free, open source.
Snap drop: web based instant file transfer between devices. Free, open source.
X-Plore: the only file manager that ever clicked for me. Dual pane that's really intuitive. Absolutely packed with features (connects with local network, cloud providers, ftp, ssh, dlna, has file sync)
The exposed metal looks like it would saw through pockets in record time. What's your experience been?