For me these are the perfect strap for sunglasses (or my everyday Ray-Ban Wayfarer Metas)
I probably like them for the same reason that others hate them; in that the leash is basically a thin coated wire / cable with rubber ends to slide on the arms of your glasses.(The large fits the Wayfarers so they're plenty big enough for most glasses too)
I really like this design as I find it unobtrusive and comfortable and, with its slightly shorter length: to the top of my shoulder blades, means I actually catch it on clothing less.
Also the design itself is smart and modern. I much prefer its look over the Cottons or neoprenes that are mostly used by rivals. That's a great look on the beach but not so much in an office or mall where these just blend in nicely.
All in all, I'd recommend them 100% and, indeed have purchased several pairs from S2as.com as I've been so pleased with both the leash and their service....and prices!
Photo attached showing leash attached - ignore the curved ear grips: they're a separate item)