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.
doo - A smart, simple app for reminders and to-dos
Simplenote - The simplest way to keep notes. Light, clean, and free. Simplenote is now available for iOS, Android, Mac, and the web.
HabitBull - HabitBull
Laverna - Laverna is a JavaScript note taking application with Markdown editor and encryption support.