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.
For hosting common files it's ok. Also it is on Android too do, great to transfer files between your Windows and your phone. But if you want better security you have to subscribe a monthly offer.
Habitica - Habitica is a free habit building and productivity application.
Dropbox - Online Sync and File Sharing
HabitBull - HabitBull
Google Drive - Access and sync your files anywhere
Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
Mega - Secure File Storage and collaboration