I'm no expert so I can't fully understand the ATA Secure erase page (it seems
to also make data irrecoverable by recovery programmes if done to an SSD).
The thing is though, if you let the current erasing process finish and end up
with an empty drive after that, you (should) be able to install Trisquel on
it regardless as to whether there's any data there un-overwritten.
P.S. Overwriting with zeroes seems to be most important for "Low level
formatting is a hard disk operation that should make recovering data from
your storage devices impossible once the operation is complete. It sounds
like something you might want to do if giving away a hard disk or perhaps
discarding an old computer that may have contained useful and important,
private information."
