On my OMs I used Hoya but I figure that after 30 years of development these will be good too. I just like an extra bit of glass in front of the lens for when I fall over! It's much thinner than the Hoyas I have on my OMs but even so the Petal Hood will need a bit of 'carving' as there is just a bit of encroachment and shadow. More to do with the hood I suspect.
I suppose I am a middling grade Olympus photographer.
I have used Pig Iron filters for some time.
Initially drawn by the name I have never been let down by substandard wares.