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.
Google Calendar - Spend less time managing your day & more time enjoying it
Habitica - Habitica is a free habit building and productivity application.
Business Calendar - Powerful and easy to use calendar app for Android including weather, widgets and tasks.
HabitBull - HabitBull
Jorte - Schedule books must be practical and has a good design.
Todoist - Todoist is a to-do list that helps you get organized, at work and in life.