I have 15' unibody alte 2011 MBP. At the moment it has 4gb ram. I was on crucial site and see I can upgrade to 16GB kit (8GBx2), 204-pin SODIMM, DDR3 PC3-10600. On crucial it costs 160dollars http://www.crucial.com/store/mpartspecs.aspx?mtbpoid=957BE069A5CA7304 on amazon its 135 and from ebay from HD-MEMORY who have over 15000 sales and good feedback, same memory is 81 dollars. http://www.ebay.com/itm/16GB-DDR3-P...4483984?pt=US_Memory_RAM_&hash=item3a736ad390 Im wondering is there any real difference in these rams? should i opt for ebay? is there any difference to crucials version of this ram and the ebays. Just want to know before i purchase anything. Thanks in advance.