Edit: …and it completely slipped my mind to thank dealbot for the heads-up on this one.
Only 3 keys this time, and for Borderlands 3.
They're 'universal' so should work on any platform, but you don't need to own the game to redeem them. These are not codes to unlock the game, they're only for receiving special loot in-game. They can be redeemed in-game or through your SHiFT Account online (membership is free).