What’s the catch? This is the best deal I can find on the internet by a fair margin. This seller has an amazon store page as well and seems to have a good reputation on both. The seller claims its a new HDD from a reputable brand and offers a 5 year sellers warranty.
I realized I probably should have added more context so I’ve edited the above post a soon as I posted.
It looks like the seller also accepts Apple Pay and credit card.