I have two of these variable ND filters with 55mm and 67mm filter threads. The filters make an absolutely high-quality impression, which is also supported by the packaging, in particular the storage box.
The filters have a scale on the aperture ring that starts at ND2 and ends at ND400. There are 8 stops in between. Unfortunately, the respective extension factor for each stop is not documented, so that the exposure time is difficult to calculate. Here, you have to get the best result by trying things out.

Review of "K&F Concept 67mm Magnetic Variable ND2-32 Filter (1-5 Stop) Set for Phone Lens Camera Mount Comaptible with iPhone 15 14 13 12 11 Series, Magnetic Neutral Density with Filter Holder" currently at £49.99:

I used this with my Samsung S20FE phone and it fit well even with case on. The filter is 67mm and fits over all the cameras on my phone easily. It has a nice smooth action for adjusting the ND level. It has a magnetic clip for the lens which is nice, but I would have liked a standard screw mount so other filters could be used.

It is quite expensive for what it is, especially as I can't attach other standard 67mm filters to it, but it does its job well so I can't really mark it down.

I received the new X-PRO filter set today and have already tested its applicability in the apartment. A judgment on the quality of the filter glasses and the combinability in a shot I still deliver ... The supplied box holds the holder + adapter rings + CPL + ND 8/64/1000. At the drawstring you can pull out the compartments and then very conveniently remove the filters. The plastic filter frames are decently sharp-edged, but not unpleasantly so, and allow you to remove and handle the filter without having to touch the glass. The tabs on the frame also make it very convenient to pull the filters back out of the holder, especially in any order. I have ordered two empty frames in 100 X 150 on the manufacturer's site, which should take my graduated filters after receipt, which I have from another manufacturer. I am curious how well this will work. If it works out, I'll have a complete system for myself, with CPL, three ND filters and two graduated filters (Soft 0.9 and Reverse Soft 0.9). Sliding the filters in and out of the holder requires some force, but is neither awkward nor imprecise. This will then also allow the graduated filter to be aligned well. The handling of the CPL filter with the insertion bracket is great, the turning mechanism is a bit rough, but precise. Screwing the adapter rings onto the lens goes very well, the threads are cleanly made, nothing rubs. Attaching the holder to the adapter ring is also a pleasure and the existing locking screw is very welcome, as the holder can be rotated relatively easily on the ring. The handling of the system has already convinced me, with "only" two slots I can live well for my needs and I look forward to the first use, in the next few days, in the great outdoors and with cold fingers. I have so far worked with round screw filters and waived graduated filters, which I now want to change. I also looked at the system from Rollei (Mark II), which can not keep up with the X-PRO from K+F in handling. Everything very flat and fiddly, offers little surface for holding and joining the parts. Getting the polarizing filter or adapter ring out of the holder again is no fun and almost impossible with cold fingers. K&F has solved this much better. Who wants to use graduated filters is very well served with the X-PRO set, who only needs gray filters, I would advise a magnetic round filter set, whose diameter is well above its largest lens, which is even faster to use, is more compact and should then not darken with several filters in parallel.

Easy to handle. I used the Graduated ND Filter with the ND1000 to take a long exposure. I haven't noticed any color issues with these filters, they are fairly neutral. An ND 32000 would be missing in the range

Easy to use,
I used the graduated ND filter with the ND1000 for long exposure.
I didn't notice any color problem with these filters, they are quite neutral.

An ND 32000 would be missing in the range

These filters are really good value for money. Originally I was just looking for a graduated ND filter but considering the great value of these I bought the set.

Very useful and work very well.

These filters are really good value for money. Originally I was just looking for a graduated ND filter but considering the great value of these I bought the set.

Very useful and work very well.

This K&F Concept graduated ND filter is a great addition to any sunset or sunrise landscape filter collection. For the price, the filter feels well made and has smooth threads and fits perfectly on my Sony lenses with or without a pre-filter. I haven't had any issues with threads as some have reported. The filter has a very smooth gradation with a smooth pivoting mechanism to align the color gradient as desired.