In reply to The New NickB:
> Have you looked at the models in question?
If you're asking that because of my comment about very little gains, The problem with things like this is they're all marginal gains tech. So you're not going to notice the difference unless everything else is optimised. And they look really hot (not necessarily a bad thing in the UK?)
If you're only looking because of the visor I think prescription sunglasses are a better option. But go to a fairly posh optometrist, I got my first prescription sunnies from Specsavers and the sunglasses made my eyes hurt. I went to a different optometrist and the glasses guy explained how, because of my astigmatism, there were a lot of requirements to make me glasses that worked properly.