As someone experienced in data recovery, I side with him that doing more than a zero write is unnecessary for 99.999% of the population. And if you needed more security, you would physically destroy the drive. There is the possibility of having relocated sectors with data that drive firmware hacking could allow you to access. In theory a drive written over once could have remnant magnetic fields that could be recovered with a electron microscope. That would require a clean room with multimillon dollar microscope and possibly months of expert labor. If an organization can do this they are not talking about it. Maybe a intelligence agency would do it if was important enough and they exhausted many other means to get the intel first.
