I've been using them for backups.
Also, there is a $5.99/mo minimum charge as long as your account is open that covers up to 1TB of storage.
I tried BackBlaze B2 and it worked incredibly slowly with restic. Not sure what the problem was.
The dev server I backup is around 80GB, has a few VMs I use to build HashBackup on different platforms, and takes around 45 minutes to backup, with most of that time waiting for my slow-ass Internet connection. My last retain/prune took 20 minutes, including repacking 22 remote files.
The other nice thing about B2 is they give you a daily 1GB egress allowance, and HashBackup uses that to recover wasted space from deleted files. They bill me $0.53 every couple of months: 25 cents/mo for storage and 2 cents/mo for egress. Can't beat it!