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.ly - Todo.ly is an intuitive and easy to use online Todo list, and Task Manager. It helps you to get organized, simplify your life, and to get things done. Create todo lists, and manage them online from anywhere.
HabitBull - HabitBull
Doit.im - Doit.
Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
The Hit List - Your life is complicated, but managing it doesnt need to be.