I've been listening to all my headphones this afternoon, trying to figure out which to purge. I'm not a big collection kind of guy. On the closed side it was pretty easy. But I only want one set of open headphones, since I can't use them as often as the closed, and I'm having a heckuva time deciding between the ZX1 and the Fidelio X1S.
They couldn't be more opposite physically... ZX1 is light as a feather with almost no clamp. As mbwilson11 says, very speaker-like, like having a couple big foam speakers resting against your ears. The X1S in comparison seems built like a tank, comfortable but heavy and clampy. Sound-wise is a pretty close call, with preference depending on the song. I'm leaning toward keeping the X1S for the build quality, but selling the ZX1 might be a trick since I don't think anyone outside this thread has heard of them.