There are more critical files that might fit on a flash drive.
gulp I would never trust critical data on a flash drive for backups. They are one step up from SD cards, but not a lot better.
Also keep in mind, SSD are not designed for long term offline storage. Many SSD are rated for only 2-5 years of integrity without power.
I assume there must be network storage backup systems that would be resistant to mass wipes or scrambling, but that may not be viable for personal use. I need to look into this more.
There are lots of options, I named a few, but they can get pretty complicated. Although there are some simplier options as well, just getting a USB HDD offsite on a regular basis can help a lot.
How complicated it gets is directly proportional to how much it will cost you if you lost your data.