NVMe M.2 drives do work with the iMac 5K 2015 and 2017 as well as the Macbook Air 13" 2015 and the Macbook Pro Retina 13" 2015 out of the box with the correct adaptor. It appears that only particular versions and brand of the adaptor works well.
The 2013-2014 Macs need a modded firmware to work well.
@danj has mentioned in another thread that adaptors might have massive CRC issues, but he did the test 1 year back. No sure if the adaptors that the Macrumors users are using are newer versions that seem to work very well.
Check out this link. Someone used a Samsung EVO 970 drive in his iMac 5K 2017 without any issues.
The HDD is upgradable without a thermal sensor if you use a temperature control app.
You can use Macs Fan control or SSD fan control. Both will work.
The SSD only version comes with a 3.5" Hard Drive bracket but not the SATA cable.
Does the 27" 5k 2027 SSD only model still have the HDD brackets installed, asked at Apple store but not much luck with an answer, they didn't seem to realise you could get a SDD only model.
John - Good question!
We'll need to wait till someone opens up a SSD only model. The OWC vid below is a Fusion Drive config so it had the drive. Even still, the brackets are the standard ones the 'Thin Series' uses so you can get them and remember, you'll still need to get the custom SATA cable anyways to add the drive.
Just notice this on You Tube, I think this will answer a lot questions about upgrading a 27"5k 2017 iMac The Best 2017 iMac Apple Doesn't Sell!
Can you add to this mac an SSD like in the above videos, but also still keep and HDD inside? So for example a 512SSD and 2TB HDD configuration.
door Andrei Birsan
Andrei, your system supports two drives one SATA (HDD or SSD) and one Custom PCIe Blade Drive (SSD only)