I have heard the S and Z series and eventually settled on the Z1s. It's not going to be a popular because it is not an exciting speaker. It's the type of speaker that you probably won't bring home if you only spend 10-20 minutes auditioning, but the choice would be clear if you really take your time to listen to all of the details and dynamics. It's also one of the more analytical speakers, and at that price point, most people would go for accentuated bass and highs, or focused vocals. But yeah, if people took the time to listen, they will find Quad speakers to be very revealing and satisfying.
My youtube vid review of the Quad Z1s https://youtu.be/kEca-2rjLik
My youtube vid review of the Quad Z1s https://youtu.be/kEca-2rjLik