This is an interesting thread about higher efficiency speakers. It is indeed the case that most horn systems do not have great time alignment of drivers. However, if the speaker is designed properly, this in not really much of a problem. The trick is to have a wide range horn driver so that frequencies from 500 hz on up to around 5,000 hz or slightly higher are handled by the horn driver. A single driver covering this critical range will make the speaker sound coherent, clear, and the drivers can be made to sound well blended. As mentioned above, the tricky part is getting a woofer with decent efficiency to match the other high efficiency drivers. There are woofers that can do this and are fast enough to work up to higher frequencies, but, they do, like all drivers, have their tradeoffs--most have low excursion so they don't do truly deep bass even when they are very large in diameter, most require a fairly large cabinet, and modern versions of such woofers are hard to find.
Also mentioned above is the use of active crossover and powered woofer to mate with the more efficient driver(s). For example, I like the Cube Audio Nenuphar Basis system that employs their fullrange driver plus a powered woofer; to me it sound more natural and tonally balanced than their fullrange only systems.
I mentioned, and so did others, the Charney Audio speakers. To be specific, I heard their Companion model with both the Voxativ and AER fullrange driver options (they have others). I liked both drivers a lot, but, my preference was for the AER driver. Pure Audio Project speakers are also modular systems with different options for their midrange/high frequency drivers. I've heard their terrific sounding speakers with both a horn-based module and a coaxial driver; both sounded very good. I have not heard the much more expensive module utilizing a Voxativ field coil driver, but, I've heard that driver in other systems and really liked its immediate, very dynamic sound.
My very favorite high efficiency speakers are custom systems utilizing new and very vintage drivers made by Deja Vu Audio in Northern Virginia. This is a retail store that also makes speakers, tube amplifiers (linestages, preamps, phono stages), and even DACs (no longer made for lack of suitable parts). Their systems typically feature vintage midrange horns and compression drivers matched to modern tweeters and custom woofers (woofers made to their specific requirements). For some of their very best systems, modern manufactured drivers that are meant to be exact copies of vintage Western Electric drivers are used and their own custom built tube power supplies are used for these field coil drivers. Right now, their most popular custom speaker utilizes a surprisingly small cabinet to house an 18" woofer (modern, custom design), a modern bullet tweeter, and a terrific sounding Japanese folded horn and compression drivers (probably from the 1960's); this is a scary good system that is a bargain at the $35,000 price they charged. For my particular taste, I like them much more than contemporary horn systems like JBL Everests, and Klipshorn, Volti, or even the Edgarhorn systems that I've heard.