Some tests carried out by the “Non-Volatile Systems Laboratory” have revealed some serious flaws with SSDs ability to be securely erased. When using standard tools designed for spinning disks, the results were understandably bad. They also tried the built-in “Security Erase Unit” command and the results of this were generally not good. After being securely erased, most of the SSDs still contained some large fragments of the test files.
Some secure erasure software would be similarly inefficient for hard disks anyway, as things like remapped or bad sectors can still contain readable data which may not be erased during the process.
The simplest solution for securely erasing any data is to completely destroy the storage media. For hard drives this means making a real mess of the platters, for SSDs it means wrecking the whole PCB, data chips and controller chips.