Answer: By design we can avoid the use of the filter in non-wide angle lens will not have dark corners, if your focal length is less than 24mm still may back to produce. 

If you rotate your ND filter past the ‘Max’ mark on the filter rim, it can cause an x-pattern, so ensure you’re not over-rotating. Variable ND filters also have limited application with wide angle lenses (they can only be used to about the halfway mark of Min and Max markings because the field of view is so broad). For a wide-angle lens, we suggest using fixed ND filters or ND2-32 or ND8-128. You can also try adjusting your focal length and reducing the density (rotating back towards the ‘Min’ mark) until the colour shift disappears. 

I have the 77mm version of this and I am NOT able to use a lens hood on my Canon 17-40mm wide angle once the filter is on. I haven't tried putting on the hood first and then trying to screw on the filter yet. That's not to say that all lens hoods won't work but for me it does not under the scenario described above. 

"X" cross on images is a common issue with wide angle lenses and variable ND filters. Physics limit the capabilities of variable ND filters on wide angle lenses.
When you enter the edge of the max range,the "X" issue may appear on your image. Because you are using it beyond its capability according to the laws of optical physics,which will inevitably cause this phenomenon.
 

By design we can avoid the use of the filter in non-wide angle lens will not have dark corners, if your focal length is less than 24mm may still return to produce.