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.
The catch is that they’re Seagate drives. Seagate have some of worst reliability in the industry and you’re buying it secondhand from eBay.
Personally I’d rather just set my money on fire.