We all are probably guilty of falling for the convenience trap here or there. But setting up the sync between Dropbox and the NAS (Synology user here) with a one-way, don't delete, don't overwrite policy is a good lifeline to have - you know, just in case...

I'm a big advocate for running a NAS, but using a service like Dropbox means there's one fewer personal device that needs babysitting.

QNAP does not seem secure at all, IMO its not worth it. I have not used the others you mentioned.

You would still need somewhere to do off site backups to.

(Edit: changed offline to offsite)