They are by PDP, but the difference, as you said, they come with he official Nintendo Seal of Approval.
I have the Hori pads...they're ok. The buttons seem better than on the PDP ones, though. Except for the triggers...those are kind of weak on the Hori models.
And I agree, nothing beats the original gamecube controllers. That said, these controllers are kind of like Amiibo for me...I just want them all, in their boxes, on a shelf. I can't explain why, I'm just a sucker for a series of controllers, especially one that has Link in it.