It cannot be used with the lens hood. In order to avoid the problem of vignetting, the outer diameter is larger than that of ordinary filters at the beginning of the design. 

To avoid dark corners, K&F Concept ND2-ND400 filters are designed in ultra-wide construction so the front side of the ND filter is one size larger than the camera lens. It is recommended to use a lens hood of a larger size. 

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. 

For this series, front thread diameter is bigger than the back thread diameter.
for example:
Back thread diameter (attach to lens): 40.5mm
Front thread diameter (attach additional filter/other accessories): 43mm
Variable ND filter size other accessories size

37mm	40.5mm
40.5mm	43mm
43mm	46mm
46mm	49mm
49mm	52mm
52mm	55mm
55mm	58mm
58mm	62mm
62mm	67mm
67mm	72mm
72mm	77mm
77mm	82mm
82mm	86mm

 

No, the lens cap can only be used with K&F Concept variable ND filters.