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Late to the party, but a few additional thoughts:
While the coupler allows 90 degree incident waves simply to pass through, sound at angles of incidence greater or less than 90 degrees are reflected into the coupled space, and subsequently returned as a kind of artificial reverberant field, or diffused (loosely speaking) back into the environment (behavior changes with incident angle of course, and the diffusion is not as even or predictable as with something like the typical 1D QRD or 2D PRD).
In a control room, this could be one simple method of breaking up some mid-range early reflections without removing too much energy in a room, or causing comb filtering effects of QRDs that are placed too close to the listening position (typical of attempted use at first reflection points in a narrow room). Of course you would have to take into account speaker locations and incident angles. Also, this implementation would not address any low frequency concerns.
They could also be used with absorption behind depending on goals and application. One example is as part of a cloud overhead, with absorption behind the grating. This is one area where they claim the enhanced bass performance. I have a couple theories as to why this might be the case, but I couldn't say definitively without some more study and testing.
In a recording room, the application would seem more obvious. With more absorption lower in the room, you can control the early reflection characteristic, yet by coupling a live space overhead, you get the added benefit of a longer-than-expected, smooth reverb tail, without sacrificing your control. This technique, while it may seem new to studio practitioners, has been practiced for some time in certain large-scale projects, including some concert halls.
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