Zu's revolutionary aspect derives first from the accomplishment of their wideband full-range driver. Without that, the crossoverless design would not be possible, or it wouldn't yield the same results. Druid and Definitions are systems, holistically designed to meet music fidelity objectives beyond what's attainable by price-competitive products.
Keep in mind that Zu pursues this stellar sound in a consistent way with inconsistent speaker topologies. The Druid is an open-cabinet system that leverages an acoustic energy management principle first developed to manage motorcycle engine exhaust for power maximization from the engine. The Definition, on the other hand, is a sealed box system, but not strictly an acoustic suspension design, as the cones move little and do not rely on the enclosed air spring for support. However, both designs, along with the sealed box Tones achieve a family sound that delivers unprecedented fidelity in compact footprints.
You're right, the Zu advocates are a relatively small population. This is a small company that invests very little money in promotion and has no dealer channel. But it is growing and had won a reputation for innovation and sensational sound quality out of scale to their actual presence in the market.
Also, Aktchi, you're correct -- from a marketing standpoint, Zu has a hole in the middle of their line. Today, Druids deliver 70% of the Definition's fidelity and quality at less than 30% of the price. And the right amp is crucial to that equation (not necessarily expensive). So there is mitigation to that gap. That is to say, $2800 Druids are fully worth, for example, $8,000 of power amplification. What you'd spend on a more expensive speaker, if put instead into better amps for Druids, would achieve much the same thing or better. But Zu will nevertheless plug this gap when they have the right product.
Sean & Adam are committed to continuous improvement, so the Zu models will never be "done." However, refinements will become progressively more incremental as has happened with Druid, in part because its the FRD that drives much of the result, and it's excellent now. You can consider their speakers "settled down" but not immune to improvement.
I've owned many highly credible speakers over more than 30 years of audiophilia. And I've worked in the business, maintained connections to it, and have heard nearly everything worth hearing at some time or other. I'm not speaking out of context when I say Zu's sound is real. That said, however, I agree with the prior comment that when auditioned by mainstream audiophiles in context of a group of decent speakers, Zu will be ranked by many as either first or last. Hearing a truly phase-coherent, transient-uniform, tonally accurate, dynamically faithful, efficient speaker sans crossover for the first time is powerfully disorienting to people who have never heard the precedents for Zu's design principles. Which is almost everyone on this board.
Phil