Paul- If you haven’t made the move to SSD yet, i suggest you replace the SATA 3.5” HDD with a 2.5” SSD, and leave the blade SSD already installed in place. You can create a new Fusion Drive with the SATA SSD & stock blade SSD. This allows you to still take advantage of the blade SSD for extra RAM.

I just did this myself on my Late 2015 iMac 5K with the 2TB Fusion Drive. I swapped the dinosaur HDD for a 4TB Samsung 870 QVO 2.5” SATA SSD and my computer feels like new! better than new!

I don’t recommend replacing the blade SSD because it’s a lot more complicated and you run a real risk of damaging the logic board.

i have a late 2015 iMac 27” 5K (iMac 17,1) and I do not have a microphone along the bottom. I am confused because other people do?