Good question. I have the Century Optics wide and ultra wide lenses and actually didn't notice all that much of a difference when I put it on my HVX200A.
I've been looking at the .75x one. Please someone correct me if I'm wrong, but the .6x lens won't allow you to use the zoom controls on the HVX but the .75x one will? So if you're doing some quick and dirty videography work you won't be able to do any movement outside of pan/tilt from the sticks?
Also how much distortion around the edges do you get from the .6x?