I'm bothered by the whole idea of putting all my data with any one vendor (with Backblaze or Amazon) and thinking you don't need a backup. I claim "RAID / Reed-Solomon / real time mirrored copies" is NOT "Backup". If your programmer makes a mistake and a line of code deletes some mission critical data from Amazon S3, then all the Reed-Solomon encoding in the world doesn't help you, the data is still gone.
What you need is a copy of all your data from Amazon S3 in another vendor lagging behind for 24 hours that is NOT real time mirrored. Maybe you lose all the customer data generated that day, but your business survives by restoring from backup. (I chose 24 hours arbitrarily, each business needs to choose their upper limit of loss where they can survive.)
A good rule of thumb for a CONSUMER is three copies of your data: 1) primary, 2) onsite backup, and 3) offsite backup. If you are a business that will lose millions of dollars if a programmer makes a mistake or an IT guy is disgruntled, add 4) another offsite backup with a totally different vendor that doesn't share a single line of code with 1-3 and has separate passwords.