Why not more popular?

I've owned many good speakers from the DQ10 days, and yes they could do bass if you had a big enough amp, say the Threshold 400A they could sake the room, to Dynaudio Confidence speakers, ProAc, and Quad ESL's. I decided to try the Spatial Audio M3 Sapphires which are OB speakers. Like all new speakers, one had to allow them to burn in and learn how to set them up properly. Reading many of the anti-OB speaker comments and their sound, is nowhere what I am hearing in my system. Clayton woofers are designed for OB speakers period, in the past box woofers have been used and they suffer bass roll-off. The tweeter in the M3's was selected to work with the woofers and the open baffle and covers a large range from the midrange to the highs up to 40Khz. Once burned in the bottom end is so good, with detail, speed, and texture, that one does not need a subwoofer, in fact, I tried them and they ruined the coherence of this fine speaker. They are nowhere near boring, they make music sound alive, open, and tonally right. They produce what you feed them, you change a power cord or interconnect or speaker cable you will hear the change big time, meaning coloration is very low as well as distortion. They rock out, they play Jazz, they do baroque, large play symphonies, the piano is dead-on right, brass and horns also. They are also just enjoyable to listen to and as my wife says that sounds live. After being with my rebuilt Quads 63's by Kent at Electrostatic solutions, and enjoying them for almost 9 years, I wanted a change, I heard many speakers at my dealer and none for the money could match my Quads and they were 12-20K. Thus my research and finding Clayton Shaw speakers and after speaking with Clayton decided to take the plunge. Clayton is honest and upfront, I wanted the X5's but he suggested the M3's as the best speaker for my room and distance from the speakers. He was dead right, the wrong speaker for a given room is a waste of money because they just won't work. While no speaker is perfect, and you can always wish for if it only had this or that, but overall the M3's is one of the better sounding speakers I've heard or owned, and they are a real value vs. sound quality. After Quads, it is very hard to listen to a box speaker, with the M3's I not only listen but enjoy the difference from the Quads, and like the Quads, they just disappear when listening. Unless you hear them you cannot comment on OB designs of the past, because what these speakers do, do right is sound real as the recording and alive like few speakers can, like panel and stats, they are an open window to the recording. They cost $5,000 and worth every penny and then some. 

"I’ve heard Emerald and several other boxless dynamic speakers at shows and they sounded good, with weak bass, and less dynamic than I’m used to".

You’re not talking about Spatial Audio speakers, they kill what you say on the faults of other older designed OB speakers. Time has marched on.