I'm using Sync.com, too, but haven't ramped up fully. A few notes:
- It can't handle Mac filenames that are non-standard in other OSes. (One possible workaround is to keep files in a Mac disk image, but there are multiple types of disk images and potential problems, all of which I haven't tested.)
- I haven't tested performance (e.g. vs. Dropbox). Anyone else?
- You can use it free, but I just bumped up to ~ $99/year for some extra features (and capacity).
- It uses end-to-end encryption, a major advantage vs. Dropbox, iCloud et al.
- There's no "app" for Linux, but you can use it in a web browser.