You can check the DDMS for details, but the code can be added to an uber account that hasn't already used the promotion, and you can get 2 free rides from LGA in any class (black SUV was definitely nice). I've had no problem getting drivers to start the fare at LGA and pick me up elsewhere.
1 code = 2 rides. Selling for $100 (seems fair considering I got over $400 of value from one card).