The iMac 5K is calibrated from the factory with a similar instrument to the Konica Minolta CS-2000 Spectroradiometer, which is a $7,000 unit that needs routine calibration itself in a controlled environment itself.
Though prolific advertising and numerous forum posts will tell you otherwise, a $169 Colormunki photometer that's been sitting on a shelf in various temperatures for lord knows how long uncalibrated, will not give you more accurate results than that from the factory even years later. This is without even beginning to consider user error involved in simply dangling the unit on your screen with a counter weight on the other side of the cord.
But of course everyone will chime in that they wouldn't dare look at their screen without using their Colormunki/Spyder/Xrite but whatever. Or that they wouldn't dream of looking at photos on their iPhone XS MAX, even though the OLED is
incredibly accurate.
