These are great glasses, and the style is slick. The interchangeable lenses are a bonus and the ridiculous case it comes in is even better. My concerns about the PIV-Lock mechanism itself is the only reason these are getting an 8 instead of a 9.
The interchangeable lenses give you the option of choosing the best colour/intensity for the brightness level you're going to encounter.
The Pivot-Lock design definning how the arms mount to the lenses is pretty intense. Although the conecpt and the implementation is really well done, the amount of pressure needed to pivot the arms in order to detach them from the lens can feel almost too much. The first time I went to change the lenses, I spent 10 minutes pressuring myself to use more and more force than I was comfortable with. I was afraid of breaking everything, but it did finally give way with a nice *snap* sound to match.
If this is your style, then yes, they're worth the cost.
Typically what you'd expect for sunglasses.
My only concern is the pivot-locking mechanism itself. Given how much force was required to latch/unlatch the arms (at least on the first try) and how they are made of plastic, I would be mildly concerned with durability. That being said, they are backed by a lifetime warranty against manufacturer defects. This shows that Smith is willing to stand behind their design and that brings a level of re-assurance to their choice of attachment mechanism.