It's a risk. it might work, it might not..... it might work but be sub-optimal. It's all unknown unfortunately.So it wont work if I buy of amazon? because I planned to buy 1 8GB one
If you consider what you know about PC building, what you know about the differences between the specifications of the individual components and the relationships between them all...... I think you are in the right place to get a well specified system.
It's going to be difficult to give you advice that you're going to understand fully, this is something you can accept or not unfortunately. We can attempt to go into detail on the why's etc, but whether it will make sense or not is anyones guess.
At the end of the day it's entirely your money though so if you want to follow your mates advice to save a few bob then there's not really a lot more we can do to help.