DDR4 2133mhz 8gb or 2400mhz 4/8gb?

[oitwasntme]

I've got an ASUS ROG Strix GL553V-DDM664T laptop and it currently has DDR4 2400mhz 4gb.I'm quite new to upgrading laptops so bear with my vacuous questions if any.

I've been offered a Kingston 2133mhz 8gb(KVR21S15S8/8) from an acquaintance of mine for just $25.I've also looked online to see that brand new crucial/kingston/a-data/etc ddr4 2400mhz 8gb costs around $60-65 and the 4gb costs about $25-30.These are my current options.

I'm wondering which will be the best bang for my buck and if it's compatible or not. I only play games on my laptop and most games i play require a minimum 6gb of ram.
Also,another question,does RAM brand matter?

 

[Darkbreeze]

If your laptop has another DIMM slot for the memory then you'd be better off getting another memory module that is the exact model number as your current one. That is the MOST likely solution that will allow you to automatically run the memory in dual channel, which is what you want since it doubles the memory bandwidth.

If you cannot get another module that is the exact same part number then you'd be better off simply going with the 8GB model your friend has because adding another module that is different, and results in a mixed memory configuration stands a good chance of not wanting to work WITH the module that is already installed. It MIGHT work with it, but the chances of it are iffy. Often mixed memory will not play nice together.

Usually when we talk about this we are talking about desktop memory, but laptop SODIMMs are generally about the same, or even worse than desktop memory, when it comes to compatibility issues.