I have the late 2013 model of the 27 inch iMac ... and it took some time to be sure that the back plug would come out and there would be the release button to get the door off so the RAM could be installed.
Installed the memory in my iMac and it works fine.
Upgrading RAM in my iMac was very easy with this memory.
Installed it on my MacBook Pro and it worked.
This works for a MacBook Pro 2012 13 in.
A run of memtest86+ confirmed that one of the new sticks had a bad block of about 4MB.
Do not works on Macbook mid 2012.
One of the pair was bad.
I know about Macs' "new RAM"/"3 beeps" issues, so I put the old pair back in to confirm that my MACHINE was ok. No problems.
Complete waste of time and money.