Question about Kingston Kcp316ss8/4

It means it's not buffered RAM, but unbuffered. I know, sounds logic, but don't worry about it. You need unbuffered RAM for your MacBook Pro anyway. But according to the specs on Apple's Homepage, you need DDR3L (Low Voltage) PC3-12800 RAM. Therefor i would suggest you the following product (also cheaper and in stock): Kingston ValueRAM (1x, 4GB, DDR3L-1600 (PC3-12800), SODIMM 204)

If you are going to upgrade to a total of 8GB, i'd suggest to replace the preinstalled RAM aswell and directly buy a Set of 2x 4GB to have the RAM work properly, as you usually shouldn't mix different RAM modules from different brands and whatnot. The following product should be compatible aswell: HyperX Impact (2x, 4GB, DDR3L-1600 (PC3-12800), SODIMM 204)