Hoya has produced very high quality multi-coated glass filters for many years. Actually, this particular filter appears to have been manufactured by the Tokina corporation - and anyone who has owned a Tokina lens will know just how good they can be!
I bought this digital filter mainly to protect the front element of my M.Zuiko 14mm-42mm zoom lens; and although small, I found it was very easy to screw the filter into place. The only slight reservation I have is that the filter incorporates a deep, threaded bezel in front of the filter glass (intended to accept additional accesories), and I'm concerned this might lead to some vignetting at the widest lens setting and at maximum aperture. Will have to experiment!
37mm is an uncommon filter size and goes some way to explaining why the price charged is so high (£15.22, November 2011). I still think that's a lot to pay for such a small piece of glass, however, which is why I've only awarded this product 4 stars.
There again, what would it cost to replace a damaged lens element...