I bought the "Unibody Laptop Dual Drive" for my Early 17" MBP a few years ago and simply migrated the native 750 GB drive into the optical bay with this splendid solution. A few years later, 2016, I did some upgrades and ran into the whole SATA II // SATA III mismatch issues reported for this product and another similar product over at OWC which affects my model of MBP. (grr...)
Initially - perfect; long-term upgrades are problematic though as there is a mismatch on getting drives which claim to be II 3Gb/s backward compatible to fit into this bay. While the 750 renegotiates and works as 3Gb/s, the Seagate STB2000102 won't negotiate backwards and is stubborn to try and push the III 6Gb/s 'gear'.
find a very concrete SATA II drive for this laptop model.