Its a great tool for starters, For teams I do not recommend. there are lots of apps that do the same, even google docs is more intelligible when collaborating and working with. But we already have OneNote, Evernote, Word Online, with lots of features way ahead Paper.
Use Paper to manage technical stuff and my team, and love it. Just the right number of features, document crosslinking and image embedding fits my needs exactly, and works for quick notes or longer documents.
- Big names like Dropbox or Google Docs should be good enough, given you've secured your login credentials with 2-factor authentication etc. They also have dedicated security teams which smaller players may not have. You can add extra security by encrypting your files before putting them in the cloud.