I have Photo Mechanic Version 5.0, build 18980 (60d39ba) installed on both my Macbook Pro and my iMac, both running on the latest High Sierra 10.13.
I the preview window, on my Macbook Pro the E key can be used to trigger external editing (as it should do according to the keyboard shortcut list) Surprisingly this does not work on my iMac, in order to trigger editing from the preview window I have to press command-E.
I cannot figure out what I am doing wrong...