Kingston SODIMM 4GB DDR4 2133MHz Non-ECC CL15 1.2V KVR21S15S8/4
Or,
Corsair CMSO4GX4M1A2133C15 4GB DDR4-2133 CL15 1.2V SO-DIMM
As far as I can tell, the specs are identical. Although, they don't exactly list the same specs which confuses me a bit.
But I don't get why the Corsair is so much more expensive.