They are cheap and they recently added an S3-like API, so lots of apps that let you point at an S3-bucket-like URL just work.

Extremely reliable and one of the most "no muss, no fuss." backups. I had a drive fail and was able to recover all of my files by having them ship me a drive with my data on it and I returned the drive for basically no expense of my own (I have several 4-5TB drives and had an old 2TB drive fail. All for $5/mo to know that I don't have to worry about backup of cold-storage files for as long as they're in business.

They are very reliable and have a very reasonable price which is hard to find these days.

Plus, their consumer product is extremely easy to set up so I can recommend it to folks who aren’t computer experts.