The presentation of the Nano-X series is very nice. It comes in a nice case (fake leather I think) with a magnetic closure and a pull strap to eject the filter from the case. It feels well built and looks nice.

This appears to be the same as the cheaper K-series, with a nicer case and more coatings on the glass. I'm not skilled enough to notice a big difference between them as far as photograph quality, and don't particularly want to test the oleophobic qualities, haha! If this magically resists fingerprints than it is worth the cost difference. If not, then it isn't worth the difference to me.

Things to be aware of:
You will not want to leave this on your lens. You cannot mount additional filters on the front of it (only the back). Lens cap does not stay attached to the front because the front lip isn't really the same size, and of course this filter does not come with it's own. The knob for adjustments will prevent you from using a lens hood, of course.
The polarizer and variable ND work together. Because of this, you need to set ND where you want it first, then the polarizer. The knob for adjustment screws down to lock the ND in place for polarizer adjustment, which is a nice touch and something I didn't realize at first!