Brian from Backblaze here: We're really transparent about our redundancy. We use 17+3 Reed Solomon across 20 computers in 20 different locations in our datacenter. You can read about it here: https://www.backblaze.com/blog/vault-cloud-storage-architect...
I have read plenty of posts from Backblaze in the past including the linked post, but I admit I also wanted to see details about the replication factor on the marketing site for B2.