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.
Todo.txt - Track your tasks and projects in a plain text file, todo.txt. A todo.
HabitBull - HabitBull
Task Coach - Task Coach is a simple open source todo manager to keep track of personal tasks and todo lists.
Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
Strikethru - Strikethru is a kind of to-do list notebook for managing work lists and staying updated with the important tasks.