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.
aTimeLogger - Application for tracking your everyday activities.
HabitBull - HabitBull
iBetter - iBetter app comes up with features to help you in fighting bad habits and developing new habits through your smartphones.
Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
myPoli - Gameified to-do list and habit tracker.