No matter whether steel, aluminium, copper or other non-ferrous metals: The "K=1" sensors have the same sensing range on all metals, i.e. the correction factor is constantly 1.
The increased sensing range is ensured across the whole temperature range, giving better protection against failure due to mechanical damage. As compared to standard sensors of this type the switching frequency of 2000 Hz means a more-than-average rate.
ifm sensors have been designed for a service life of many years. This is also reflected by the details. For example the captive laser type label means the units can still be clearly identified after years of use.