It is the recreation of the martial arts of western Europe based off of the remaining living traditions and the many manuals that have survived. I think they have done a good job and the need to critique the material for functionality because there are no living "masters" has developed into a really interesting scholarly and applied testing approach. Coming from another weapon tradition (kali) I can absolutely see the usefulness of this. I have crossed (training) blades with some HEMA groups and can say that they are absolutely producing good functional fighters. Better IMO than many of the Eastern traditions which have living traditions but don't fight the art anymore.
Your mileage may vary as HEMA is probably even more dependent on the instructor than most other arts are.