I have costa's, though a different model. Fathom is what fits me.
That said, frame is all about getting the right fit for you, so it's different for all of us. Want it to fit tight around the upper part especially, and not let light in from above. On the bottom end, tight fitting feels good but the lesser that gap, the more fogging you get.
What's reviewable is lenses.
And I LOVE my Costa lenses. I have green mirror (amber base) in 580 glass. My only complaint is that they're a bit dark, I think they're only 10 or 12% light transmission. So they're for fairly bright conditions and great for that. For low light, I have a separate set of glasses (Maui Jim with HT lenses).
Get glass, NOT plastic.
Negatives of glass:
1. Impact resistance/protection.
2. Weight.
3. Tend to fog.
Positives:
1. MUCH BETTER OPTICS.
2. Thicker polarizer = better polarization.
3. Won't scratch very easily at all.
Maybe my eyes are more sensitive than most, but the better optics is what I go after, and I clearly see the differences. I think it's important for fishermen especially. If I'm gonna spend that much on shades, I'm gonna get something for it because polycarb is polycarb, and as long as they're ground or molded and not stamped (like gas station cheapies), they all provide similar optics. Poly costa's won't provide sharper images than poly from any reasonably reputable company that charges far less.
Maui Jim, Kaenon, and a few others have developed plastics which fall between polycarb and glass as far as optics (and everything else, too). It's similar to the stuff most modern eyeglasses use. If I was gonna go non-glass, I'd look there. Costa's plastics are regular polycarb, I think.
I haven't been able to compare the 400G to the 580G. 400 nm is approaching UV and most quality sunglasses block that. The 580's have an additional dopant that absorbs light in a narrow band of yellow wavelengths, which mostly it makes the reds and greens really pop. In the absence of a wavelength, your eyes and brain emphasize the other colors near it on the spectrum. It works, but it's somewhat of a parlor trick. They say there's less eye strain, and that may be true, I dunno. One thing to note is that if driving with them on, at stoplights, on some I can't see the yellow light at all, on other lights it's actually enhanced. Must be which LED they use in the lights.
Maui Jim uses a similar dopant, and an additional one in the light blue band as well I believe. So in addition to reds and greens, dark blues and purples pop as well. Costa and Maui are the only two that I know of that use the dopants for color enhancing effects, rather than aim for a fairly smooth transmission curve in the visible light spectrum. Some people don't like it, others love it. I think it's cool, but wouldn't demand it or say it's worth a great deal of money.
