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.
PastBook - PastBook is an online service that allows you to create your own beautiful photobooks and share them with friends and family.
Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
Kemento - Your life stories captured, forever
HabitBull - HabitBull
Timehop - Your digital life history