I certainly wouldn't blame you for returning it, but it still blazingly fast. My early 2013 15 inch rMBP hardly tops 415 write/455 read speeds and I certainly haven't noticed any issues. If it doesn't fall within Apple's thresholds for replacing, return for cash and buy another one. Of course, you may get the same thing.
Either way, enjoy!
You are certainly correct. A new purchase may end up having the same SanDisk not Samsung.
I am trying to find out when did the Samsung Macbook owners take their shipment. I also work with Apple as a component supplier so I will check with Apple folks if they have stopped sourcing the SSD/controller from Samsung and only do business with SanDisk. Which, if true, will make it pointless to return.
Thanks for all inputs!
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Sharing with everyone the benchmark of all possible MacBook SSD options:
http://www.harddrivebenchmark.net/ssd.html