I believe Blackblaze also removes the backup after some number of hours, so if you don't download the backup by then, you're in big trouble.
Crashplan also allows external and network drives to be backed up.
Also curious: have you had to restore with CrashPlan, and if so, how has that process differed?
I found 1-2 times a year, when initiating a backup, the entire archive I had disappeared, as in, my computer would start to send all of my files all over again. This was very disconcerting.
I never liked seeing all files on an network drive disappear just because it was unplugged.
The final straw was when I attempted to restore a large archive, and saw the download speed was so slow, it would not finish before this restore was removed on Backblaze's servers.
Crashplan, has had zero issues over 2-3 years now. I've restored large files without issue, they store versions which I don't even need/want, and the desktop software works very well. Highly recommended.