Transparency note: The product was provided to me free of charge as a review sample, free from any influence or expectations. My review is based solely on my personal assessment and experience with the product. Review: For those quick readers, I'll give you my review first. Below I'll explain the details of my decision-making process and my impressions of the product. I'll deduct only a minimal point and award 5 stars, rounded up to 5 stars. My only criticism is that the filter is a bit stiff to turn, i.e., its operation when screwed onto the lens. I hope this improves over time. No, it's not stiff to turn, but it is a bit stiff; I expected a somewhat smoother movement. Build quality: The slim frame is of very good quality, precisely crafted and painted. I appreciate slim filters; they sit lower on the lens and therefore don't limit its viewing angle, especially with the wide-angle lens. Slim filters can have the disadvantage of being difficult to handle because the grip ring is very thin. It's helpful to have a non-slip grip, and that's exactly what the K&F filter is. I can grip the filter very well and see without any problems even with wet fingers. The glass in the filter is very high quality: optical glass, very precisely crafted and completely flat, and also multi-coated. First, hold the filter in your hand and look through it, preferably against strong contrasts and straight lines, such as a facade. Here you can see that you see no interference. I detect no distortion whatsoever; the image is completely flat across the entire surface of the filter, and I also see no color distortions; I'm very satisfied. It's no different when I screw the filter onto my lens, but here comes another aspect: possible reflections, which are precisely what a polarizing filter is supposed to eliminate. In terms of the image effect, this is absolutely undeniable, be it on water surfaces or on windows; reflections are suppressed very well, as expected. But there's another aspect, and that's the reflections on and behind the filter towards the lens when backlight from small point light sources hits it at an acute angle. I didn't observe any reflections here, which speaks for the filter's very good coating and glass quality. I was very pleasantly surprised by the filter's packaging, starting with the attractive outer packaging in a high-quality slipcase. Inside is a folding case with a magnetic closure; it's very stylish and practical, significantly higher quality and more elegant than the widely used plastic boxes. Conclusion: At just under €150, the K&F polarizing filter isn't exactly a bargain, but it is reasonably priced in the truest sense of the word and clearly positioned in the premium segment. The build quality itself is just as impeccable as the optical imaging performance of the lens. The included case is very attractive. Only the somewhat stiff adjustment of the alignment slightly detracts from the overall impression, so I deduct half a star for that. In the overall impression, this plays only a minor role and leads me to an almost unconditional recommendation to buy. Thank you for your attention in reading my review. If you'd like, please feel free to give me feedback; I'd be delighted to hear it.