The NiSi SWIFT VND MIST Kit performs exceptionally well through the test used for both stills photography and filmmaking. The press-on fit system worked well in practice, especially once you get familiar with it and trust the quality and durability of the filters and fit. It essentially allows for quick swaps between filters with a fit that makes it perfectly suitable for the more mobile nature of filmmaking, where the convenience of magnetic filters can be an issue.
I did find that the push-fit style was a little odd to use at first, although, after a short time, you do get to trust the quality and ease of use. With the filters mounted on the lens, fitting and removal is easy, although it is still a two-handed job to ensure a snug fit.

NiSi Swift ND4 only

NiSi Swift VND and ND 4 stacked at 24mm
When it comes to optical quality, the True Color technology of the VND ensures natural tones and bright colours without unwanted casts; this is a big selling point of the NiSi filters. Considering the cost of the filters, this would sit them in the mid-range. However, this VND comfortably equals the likes of the LEE Elements range. In this test, I used the VND on the Sony 16-35mm, and the optical quality shone through with no vignette at any of the focal lengths.
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No Filter WB Daylight
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NiSi Swift ND 1
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NiSi Swift ND 2
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NiSi Swift ND 3
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NiSi Swift ND 4
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NiSi Swift ND 5
If you add the ND16 on top again, the colour quality is an excellent landscape option. Again used on the 16-35mm, the quality was superb, but as NiSi highlights, Vignette will appear at the wider end, and around 18-20mm is the point where it disappears.

NiSi Swift All filters stacked at 24mm
The Black Mist filter is a must-have filter at the moment and adds a beautiful diffusion effect, though with all three filters stacked, there is vignetting below 35mm. The influence of the vignette is slightly more than I had anticipated, but remove the ND16, and you can widen that field of view.

NiSi Swift Black Mist Only