As you already realized i shared pictures where the Ray Masters company was mentioned recently. They are producing slot filters, and i using their products pleased, since 3 weeks ago.
I just found them accidentally, when i looked for graduated ND filters through the web. Ray Masters started only a few years ago, but they already have a wide variety of filters. They advertise their products as ND filters without colour cast. I have a doubt about this for first, but after I saw some video review and used this filters actually, I can say there is really no colour cast when using them. The company selling their filters in different sizes and different intensity. They have an own filter holder system with different sizes of lens rings. So far the Ray Masters products are still cheaper than any other big brand on the market. When using the filters, I found only two negatives. First there is no option for a CPL filter yet, and second, it’s easy to scratch the filters. This scratch problem is not that big as it sounds. Against the glass basis filters (where the ND layer is located on the surface of the glass), the Ray Masters optical resin filters are made with the ND pigments in the structure, so you cannot damage them with a simple scratch. As the filters comes in a small paper box, I strongly reccomend to buy a soft filter holder pouch in the same time.
By the way if you order any of their products to the countries of the EU, the shipping is free and it doesn’t depend on the value of your order.
Don’t hesitate if you are looking for this kind of filters and check their website and social media accounts:
Original Facebook article: https://www.facebook.com/ophotography/posts/2041944319373718