The Techlite glass lenses make a HUGE difference for me. I experience zero eyestrain wearing these bad boys. I wear my optics a lot whether driving, hiking, just being outdoors so not having to deal with eyestrain after wearing sunglasses for a long time is great. The extra scratch resistance of glass is a huge plus in the long run since accumulated scratches on the lenses is part of what causes eyestrain. This is my first pair of Smith sunglasses (worn Oakleys for exclusively for over seven years) and they are definitely a keeper. I would say that I would only switch back to Oakley if they made a more superior glass lens.

I traded my usual tried and true Julbo Nomads for a pair Smith Moguls on my last expedition. I decided to make the change for three reasons: 1st, the Smith Moguls fit my face well- which is key in blocking out solar rays and snow reflection, 2nd, because of the polarchromic function, and 3rd, the wider side frames blocked out reflected light.

I found the polarchromic function subtle- that is, the difference between bright and overcast conditions didn't change the lens tint a whole lot- but this doesn't really matter since I found the glass lenses crystal clear and the tint appropriate in all light conditions. The hinges on these glasses are bulletproof, and they survived my expedition abuse well, including a number of drops from head height.

As for durability, I found the lens almost impossible to scratch, but the silver accent on one side of the frame fell off the first week of wear. We'll see how good Smith's warranty is.

This are nice glasses but don't expect much from the Polarchromic feature. I guess there is some adjustment but is not very perceptible.
I used my galsses for a ski trip and the silver decoration on one side fell. There's another review claiming the same problem so I guess Smith has a durability issue with this.
No complains on the lens though, they are great. Frame is nice and stylish and serves its purpose to cover well the eye area and avoid reflection form the sides. But having to loose that on my fisrt week of use made me angry! Fortunatley you have Smith lifetime warranty, and better yet you have Backcountry.com warranty!