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.
Taskful - Deadlines, meet your match.
Habitica - Habitica is a free habit building and productivity application.
Calendarist - Time blocking companion for Google Calendar
HabitBull - HabitBull
Centered - Centered helps you get into a Flow State faster and stay there longer so you can do your best work.
Todoist - Todoist is a to-do list that helps you get organized, at work and in life.