I know Zu's full line and have been a customer/user continuously for the past 17 years and counting, having had three versions of Zu Definitions in that time, and three versions of Druid each model concurrently in two systems. People find me here and if they are in Southern California, more often than you might imagine ask if they can bring something to compare to items in my systems, including Zu. I had a request from someone to bring a pair of NSMT to listen to so that's how I know. The underlying principles are easily researched wrt to each company's PoV and codified approach to speaker design.
Phil