I ordered the K&F Concept Nano-X PRO Series UV filter for use with the Pentax HD DA★ 11-18mm F2.8 ED DC AW lens. As a general rule, I often use high-quality lenses without UV filters. Ultimately, quality decreases when glass is added to the light path. However, if you have dusty weather or rain, using a UV filter is definitely an idea as you can rub the filter with a cloth to dry it and remove dust. Even if the filter is scratched, the front element of the lens is still intact.

Next, let's talk about filters. K&F Concept Nano-X PRO Series UV Filters come in very fine packaging. The filter is inside the bag, and some are made of genuine leather. The clasp is magnetic. There is a ribbon on the side of the bag. Pull this and the filter will slide out of the bag.
A cleaning cloth and cardboard stand (?) are also included. Hmm, I don't understand what that means now. Perhaps it is intended as a presentation opportunity for dealers?
The filter is "made in China". The box has the address of the importer from Germany.

This filter can be easily attached to the Pentax HD DA★ 11-18mm F2.8 ED DC AW lens. I have nothing to complain about. The Pentax HD DA★ 11-18mm F2.8 ED DC AW lens will not be in the shadow of the filter. The quality of the filter is also very good.
I took some test photos with and without the filter and found no negative effects. Under normal conditions, I don't think the image quality will deteriorate that much. If the sun is at a right angle, you may experience light reflection issues in backlit images. But that would be a common problem with lens filters.

Conclusion:
The filter is really good. The 82mm filter currently costs 149 euros, which is not a bargain. After all, it doesn't make sense to buy a lens that costs around 1500 euros and then screw a cheap filter onto it and reduce the image quality. I give the filter 5 stars.