Customers most agreed on the following attributes:
Excellent optics for such a thin lens. [...] I've used it almost everytime I shoot.
The only thing that really bothers me is how stiff the rotation is and how small the ring grip is sometimes leading to fingerprints on the element. This being said, these issues are part of how they made it so thin, so it's a trade-off, one that is easy to make.
There are availabloe equivalent filters which provide the outer ring, with the sacrifice of thicker construction but greater versatility