I've used Backblaze for years and never had a problem. There's no upload file/data limit, but downloading it back can be slow. There's an option for them to mail you a hard drive but I never tried it.
When backup excluded some files, they blamed antivirus software and recommended to go without.
They actively deleted their only backup because the client couldn't read the original files (which was due to disk error).
They admitted that there isn't any guarantee or even effort to make the backup consistent - after asking me to explain the concept.
The only reason I still have my data is because of the very expensive cleanroom disk rescue that they of course refused to pay for - because why try to do what you can to compensate for failing at your only job?
However, when referring to Backblaze, I think most people here refer to their nice (and cheap) S3-like cloud storage solution, which works perfectly with the likes of restic, rclone and friends. That's probably what you should use if you care about control.
Would not choose Backblaze if I was choosing today.