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.
Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
Habitica - Habitica is a free habit building and productivity application.
Remember The Milk - Remember The Milk is a task and time management application for mobile devices.
Things - Things is an easy to use task manager.
HabitBull - HabitBull
TickTick - TickTickis a cross-platform to-do list app & task manager helps you to get all things done and make life well organized.