I have had these sunglasses for several weeks , finally had some sunny days to wear them. Contract and clarity are excellent. It has been several years since I had purchased quality sunglasses (I had been confined to Rx lens but following eye surgery I can now see clearly without Rx lens. These sunglasses are much better than any Rx glasses I have ever owned.)  I was torn between ordering gray versus brown lens.. I went with the brown and feel I made the correct choice.
The glasses come with an extra set of lens to use on low light days. Note that the spare Sport Flex lens are not polarized.
I also ordered a set of gray lens but haven't tried them out yet. The brown lens works so well I am thinking I should have moved up to the Blue or Silver  Reflex spare lens that are available (see Native's web site for details)

The only negative ,which has since been overcome, was the initial difficulty of changing the lens. Once I figured out how to switch lens it is no big deal , I just had some problems at first. If I had a video camera I would do a Youtube video to show how to change the lens (something I wish I had access to the other day)

Given the warranty offered my Native these glasses should give me good service for years.

GO NATIVE!