I agree that it’s more complicated even than I suggested. What I meant is that if a logical sector is used and then it becomes unused and then it becomes used again then it must be written to and in order to write to it, it has to be erased.
It is much more complicated because each time you write to a logical sector, it can be remapped (wear levelling) so that the same underlying physical sector is not written to each time.
So basically SSD is a nightmare from a security perspective.
I thought though that TRIM is supposed to deal with that.?? But then in that case I don’t think you want software like the above writing to unused sectors before they get TRIMmed (since writing to them could cause a remap).