hdparm secure erase runs on the drive controller though, the "hdparm" utility just initiates it? So it's not depending on whether the OS can or cannot see specific sectors. At least that's my understanding.

Even with vendor specific forensic software it is unwise to trust the relocated sector mapping is handled cleanly. A cheap XGecu T76 Programmer can pull orphaned data fragments off most flash chips completely bypassing the drive controller.

In this case, the other posts suggesting a hammer is not sarcasm. =3