Since posting this question I bought and read Elena Danaan's book A Gift From the Stars: Extraterrestrial Contacts & Guides of Alien Races. Among the many species recounted from her very knowledgeable Pleiadian guardian Thor Han, is a short note about the Men in Black. I'll include it here in full from page 156, welcoming further corroboration to this thread from other credible sources:
The so called "Men In Black" are cybernetic life-forms controlled by Ciakahrr working with the US government's secret divisions, usual accompanied, in their visits at your door to intimidate you, by a true reptilian shapeshifter. Such synthetic creatures are also infiltrated by great numbers in Terran societies and the way to recognise them is similar to identifying a shapeshifter. To these criteria you may also add a peculiar synthetic smell, unrefined features, no fingerprints, and faint or artificial looking ears. They are also named "Horlocks" and when they are not of the above, they are Terran humans under mind-control. In order to dissuade witnesses, they use mind-control (a reptilian speciality) and threat by fear as psychological weapon. They move in black cars and black helicopters, and are assigned to underground facilities.