I’ve never really been a fan of protective filters; no matter how good a filter is, it’s still an additional layer of glass that the light has to pass through. That being said, when I got my X100S, I felt that I wanted extra protection for the lens, since you can’t replace it if something happens to it.
I wanted a high quality filter and B+W seemed to be the way to go. Since the lens uses a small 49mm filter ring, the cost isn’t that great, even if you go for quality. I definitely wasn’t disappointed. When I first picked the filter up, I couldn’t even see that there was any glass in it, no matter how I turned it around it just looked like a metal ring. I haven’t noticed any discernible loss in image quality since using it either, so this comes highly recommended if you want to add some extra protection.