For pure reading of text it provides minimal benefit (color highlighting and cover art, mostly) while costing contrast ratio and dollars. Especially since some devices (e.g. Kobo Libra) are now offered only with a color display, I can see why someone would call it a gimmick. I personally view the reflectivity of eink as the entire point and thus have no interest in it.
That said, of course if you want to view color content on an EPD then it is quite necessary and not a gimmick at all.
That said, of course if you want to view color content on an EPD then it is quite necessary and not a gimmick at all.