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.
Habitica - Habitica is a free habit building and productivity application.
Sectograph - Sectograph app enables you to create a visual event tracker to keep track of all your upcoming events and due tasks right from the home screen.
HabitBull - HabitBull
Power Planner - Record homework and class schedule.
Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
Dreamie Planner - Dreamie Planner app contains a built-in diary through which users can write important details about their daily tasks and can send the content of the diary to their friends and colleagues.