I prefer Clip in filters to traditional to lens screw type because once the filter is in place (simply remove the lens and drop in front of the camera sensor) you can use it with any lens. You don't need multiple filters for each different lens filter thread size. And for some ultra side lenses, where there is no option for a front screw filter because of the bulbous front element, these are really the ONLY option.

I use mine for long exposure photography with with ultra wide angle lenses that do not allow for screw or drop in filters, without having to buy bulky and expensive front element adaptors

This clip in filter comes in this steel protective case (shown in photo).  I am also selling my ND16 (3 stop) and ND64 (4stop) versions of the same style filter, but listed separately. I use those for off camera flash portrait photography where the ND kills ambient light enough to mean I don't need to use HSS on my flash, which in turn means I can use much smaller, lighter and cheaper low powered strobes like the Godox AD100 Pro.

These filters all cost me $110 each plus shipping (see for yourself at stcoptics.com), and they are in perfect condition.