I purchased a pair of Flex Spex last time I was in Mammoth replacing a set of flip focals that I had been using for the last few years. The flip focals kept falling down when I would take a long step down, like stepping off the rails on the trail to Hot Creek. Plus they always had that geeky look so I would bring a second hat to wear after I was done fishing. I first saw the Flex Spex while browsing the Orvis site but I kind of wanted to get that hands on feeling before purchasing. I asked about them in the Troutfitter this spring, showed the owner the web site. They saw them in person @ a fly show and currently have them for sale. So far I've been satisfied with them, they are a bit more expensive than the flip focals @ $29.95.
http://www.flexspex.com/index.html