If you buy the $50 option, you'll get 2 keys, yes. You might gift it to a friend or, if a friend is interested in this game, split the money with him.
The $50 option also contains keys for 4 cases (2 per account, can all be redeemed on one) that contain rare armor - this is just a skin for costumization and offers no in-game advantage. You'll also get 1000 In-Game credits, which are also used to unlock weapon and armor skins.
The $25 option only contains the key once, with no additional bonuses.
However, both options will allow you to play on 25th January. You'll get a key via e-mail (send to the same address you used for the Paypal Payment) and you'll be able to download the game on Steam.