If a creature enters the battlefield as a copy of a face-down creature (or if a token is created that's a copy of one), that copy has the same characteristics as the face-down creature (in this case, it's a 3/3 creature with the two abilities and no other characteristics), even though the copy is face up
Most decks run both if theyre aiming for that win condition, but Exsanguinate is positioned much better in the current metagame, where gaining life can often grant you another whole turn that you wouldnt have otherwise had access to
Will Errata Cards Be More Collectible
Rush: You can challenge with this card the turn its played
In short, they make your brand easier to remember, understand, and believe in
This is likely a reflection of its cheaper price