I guess it's going through:
https://www.digitec.ch/de/s1/QuestionAndAnswer/in-der-beschreibung-steht-der-m2-slot-sei-bereits-belegt-eine-bereits-vorhandene-speicherkapazitaet--127717
The slot is not occupied.
If you go to the manufacturer's page of the two models, you will notice that the BEH2 supports 2 internal drives, the BEK only 1. This is probably why the BEH2 case is higher. But I can't explain the price difference either.
The power supply is heavy and is a bit (~5mm) longer than the NUC case (~130mm) and about 50x30mm in profile. It looks like the typical laptop power supplies.