Well... I did note a normal (though very powerful and highly talented) human mage NPC pulling it off at some point of the story, and there it was not commented on. One of the other players also had a warlock teleporting away from a scene included in a rather notable part of their character's back-story. There have been multiple other descriptions of it being done already, is what I am trying to say. (Ixion excluded here, Draigen - who was not explicitly told who or what even is -, too.) And humans are generally inferior by their magical abilities to deigan, dragons, xuhrl-njok sprynes (?) and a number of others... I had figured it would be the kind of thing which could be somewhat safely performed once from full magical reserves by a handful mages in Rodoria, and with a very high risk by around dozen or two others - so very rare indeed, but not mythical legendary scale of rare.

 - I'd expect Gerald's Shadow Image to be at least of the same rarity, if not rarer spell to be pulled off, by the descriptions.