Although I'm an avid photographer, and have used several different types of filters, this was my first time experimenting with a square filter like this one. The quality of the glass seems high, with no noticeable distortion, and the filter holder keeps the glass close enough to the lens that there weren't any strange reflections or flares visible. The photograph I've posted was taken using the ND1000 filter in bright daylight at ISO 100, f/2.8, and 1/4 second. This is a very dark ND filter, and will block a lot of light. I do notice vignetting at the outside corners of the image, but this is likely due to my lens (Olympus 12-40mm Pro f/2.8) rather than the ND filter itself as the darker image would naturally draw out those flaws in the lens that diminish with brighter exposures, and the consistency of the vignetting is congruent with a circular lens element rather than with a square filter.Here's what I liked and didn't like:Positive:1. The filter itself is of high quality glass with no noticeable defects or inconsistencies2. The adapter rings provide a wide range of lenses to be attached3. The mounting system allows for two filters to be mounted simultaneously4. The mounting system can be quickly attached and removed with the press of a button5. Filters slide in and out easily, but fit securely in the mounting system6. The case for the ND filter and the overall packaging is nice7. The ND filter is clearly labeled on one edge so you know what filter you're working with8. The instructions are clear and helpfulCons:1. The mounting system doesn't always clip on easily. This may just be something I need to get used to, but I wish there was a clearer *CLICK* when it locks in place2. The mounting system is secure, but it is released completely with the press of a button. While convenient, this could lead to an accidental release of the mounting system and whatever filter you have attached. In my case, I accidentally bumped the release button, dropping my ND filter onto pavement where it shattered. Some sort of sliding lock in addition to the button would be idealPreferences (These are things that I don't prefer, but that may be a better or worse fit for you):1. The mounting system spins freely on the front of the camera. This may be helpful for some people, but I would prefer that it was fixed, or at least allowed me to set it to fixed and then unlock it to rotate2. There are no mounting points for an eyebrow, barn doors, hood etc. These aren't essential in every situation, but you would need an additional matte box in some situations. Making these accessories available would be a great upgrade