Maybe a little off the subject, but I just don't get how someone can spend so much money on a Canon L lens like the 16-35 II & then buy the cheapest filter they can find to put on the lens! I mean I like a great deal just as much as the nest guy, but at what cost to the IQ. The whole point of spending the extra money & buying an L is for the superior IQ. Why wouldn't you do the same & spend the extra on the filter that you put in front of that expensive L glass??? It makes no sense to me.
A valid point, but as a person who normally uses good quality (I typically use the higher levels of Hoya filters - Pro1D or equivalent), I can certainly attest to the fact that the advantages over premium filters (beyond the better Hoya level) are going to be imperceptible to almost every eye. Just because a more expensive product exists doesn't mean that I blindly buy it. In the case of the Haida, I did the research, looked at a lot of pictures taken with it, then took a flyer on it. I had a great experience with the first, enough so that I bought a second in another filter size that I have been equally pleased with. In fact, if I'm not mistaken, I think Haida is actually using the same glass manufacturer as B+W. Because of that, I have not problem recommending them to someone else.
BTW, I tried a circular polarizer filter from Haida when I switched to an 82mm filter size. Didn't like it at all - not because of the optics, but because I found the rotating ring very stiff and virtually unusable in the field. The seller replaced it with a second copy, but I wasn't crazy about it, either. I ended up spending the money on a Hoya Pro-1D filter which I'm perfectly happy with. I certainly won't recommend that Haida CP to someone, but the ND filters I've had great success with.
I would rather spend a few extra dollars for a B&W then buy from a company that the workmanship is hit or miss, just like you described with your Haida filters. Buy it once & you don't have the hassle or expense of returning it & getting something to replace it. I'd rather not waste my time or money like that. My original comment was directed at the optics, but overall craftsmanship & quality is very important as well to me. I want the products I buy to last & don't want to have to return the item or replace it in a few years down the road.