Redeem your keys on multiple platforms to go into your one linked SHiFT profile. Note that Nintendo accounts must be linked before it will work on that platform. You don't need to own the game to redeem them. These are not codes to unlock the game, they're only for unlocking chests to receive special loot. Kudos to dealbot for the heads-up. Direct link to redeem at SHiFT is https://shift.gearboxsoftware.com/rewards.
3 x keys for Borderlands 3 - expires 5:00am AEDT, 12 March
5 x keys Borderlands - expires 6:00pm, 23 March
5 x keys Borderlands 1 - expires 7:00pm, 24 March