How do you be certain that ShredOS or any other component does its job? You can always physically burn the drive, but make sure you actually watch it turn to slag.

You have to trust the SSD firmware. And if you don’t, just add your own layer of encryption and manage the key yourself.

Drives which support doing this in hardware have a block just for storing the key. Because it’s not often rewritten, it doesn’t need to go in the pool of blocks that can get remapped.