Just to reiterate, both of those (hemp hearts and flaxseed) only contain ALA, while what you're generally looking for is EPA and DHA. TFA also explicitly mentions it's only talking about EPA.

This is not to say that they're unhealthy of course.

EDIT: see the sibling comment by code_biologist, it's much more comprehensive than what I've written.

Your body converts ALA into EPA and DHA, however, so plants are fine sources of both.