When using very wide angle lenses such as the Laowa 15mm, Nikon Z 14-24 f2.8 S or the Olympus 7-14mm, the extra adapters you need to use in conjunction with the K9 holder make it difficult to use the standard 90mm magnetic CPL.
To get around this, we have developed a special slide-in CPL so that photographers with these ultra wide angle lenses can still use a CPL with the K9 holder.