Definitely not a legitimate grill. (Also note the secret mark is present.)
I am certainly not an expert on grills, but to expand on my earlier comment:
Beyond the basic ID of the stamp/grill, look at how the grill and the cancel interact with each other. Here is a scan cropped from a full cover, note how the cancel does not quite hit the bottom of the points. I did not see this feature on your initial post and knew it needed closer examination, which came very fast from others.
The point being to be skeptical of grills and look at every aspect of the stamp in determining its ID and genuineness. Both grills and cancels can be faked of course.
Lastly, I like your images showing normal exposures of the front and back, then an exaggerated scan of the back. The good images make for good responses!