I guess it's really safe cause it's open source, you can make notes on your habits but don't really do that. Its simple. Really fast. Haven't found a way to connect it to notion. In general it's a great app to track you habits. Does its job. Not more, not less.
HabitHub - HabitHub is a great mobile app that helps you to plan your daily schedule to organize your life.
Habitica - Habitica is a free habit building and productivity application.
Way of Life - Habit tracking on iOS
Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
HabitBull - HabitBull
Goal Meter - Goal Meter is an elegant mobile application that helps you to change your habits and maintain your focus at work to reach your goals.