That's fine. The polarizing filters also have a rotary thread on the front where the filter plug-in system can be attached. 

Hi, the holder can hold 2 square filters + 1 Circular polarizer filter 

I've never used Hoya ND's, but I have GOBE, KERNEL, ZOMEI, and K&F ND filters. Out of all of them, I like the K&F the most because the colors look great out of the camera and they don't create a vignette around the edges like some of my other nd's which I hate. Because of the great out of camera colors, it gives you more to work with on post-production when you shoot on a flat profile. Also, I've used them during night photography on bulb mode to do light painting and the 4 - 6 stop ones work great for this. Overall, I think for the money the K&F filters are worth it. Awesome product! 

hello the K&F Concept Slim UV Filter + Slim Circular Polarizing Filter (CPL) + Neutral Density Filter + Slim FLD does not work for work for the solar eclipse 

If you polarizing filter is square and size is 100X100mm, the hold is okay for you