RAID is not a backup solution. If your filesystem is corrupted in software (or you just mistype and delete something important), it will happily replicate the damage across all of your drives.
Personally I feel recommending RAID to home users is generally a bad idea. It gives a false sense of security.
Depends on the file system implementation. Smarter RAID implementations, such those integrated into ZFS, will not be easily taken down.
In addition, RAID does not require you to use local devices. I agree, however, it is not a backup solution, and I did not claim it was. I merely stated RAID is how you deal with drives dying and taking everything with it. Backups is how you deal with RAIDs or entire locations dying, ergo, offsite backup.
And multiple Plug installations seems to cover the concurrent offsite sync part of that.
I setup unRaid for my wife's photography business. Haven't had to deal with an HD failure yet though so I can't vouch for it. Might be worth looking into yourself though for a cheap backup solution.
Personally I feel recommending RAID to home users is generally a bad idea. It gives a false sense of security.