You do know the dlc will only work for the original gamertag associated with those purchases. You will be able to see them in memory, but will not be able to play them unless you do a license transfer using the original gamertag
20GB isn't much space in the first place, and you don't get even close to the full 20GB to use for your games. About 8GB is used by the system to play Xbox 1 games and to store system updates and other system files. You only get 12-13GB to work with.
That said, if your Xbox is old (not the slim model) and you need a HDD for it, this auction is a very nice option. 20GB HDDs went for about $50 new, but now, they go for about $20 on eBay. Just bid accordingly.
@seller: Sorry if I seem rude. I'm just helping people make informed decisions. You would actually get more bids if you included more warnings and other related information, because people who are scared to bid will feel more comfortable. Convenience goes a long way!
you know that this stuff only works for the account it is downloaded on and really for offline play. Seller can just take the licenses away and the dlc may not be good anymore for online play.