No, you don't understand. An SSD isn't like a magnetic drive - when you "overwrite" a block with zeroes, what actually happens, due to wear-leveling algorithms, is that a different block of memory is written with your new data and the old block is put on a list for eventual reuse. This is how SSDs mitigate the limited number of write cycles inherent in flash memory.
It is true that doing the "clear all" in diskpart will make it look as if the whole drive was zeroed out, but 1) specialized software would be able to locate much if not all of the old data and retrieve it, and 2) it would not bring the drive back to original performance.
The "secure erase" command is specially recognized and tells the SSD to erase EVERY block of memory it has, whether it is reserved or not, and clears the allocation tables. In effect it brings the SSD back to a factory state, returning full performance.
Even using programs such as DBAN, which overwrite zeroes or other patterms, won't really remove previous data and they won't reset the SSD's allocation tables. You need to use a program that issues the ATA "secure erase" command to do that, and diskpart won't do it.
