I tried my "DAAD test". I have DAAD acoustic devices, two columns ca 3 feet high, one side diffusion two sides absorption so you can turn/tune them to the room. I placed them with the absorption towards the speaker, on the line from the speakers to the first side wall reflection points. I found the reflection points with the help of my wife, holding a mirror.
Sonic result? No big improvement - I thought. But not clear. I only have only one pair of these columns, and when I move them to the sides, I missed the positive effect they have standing at the back of my speakers, tuning the reverberant sound down. So maybe I need another pair.
A big plus is that with DAADs and similar ’smart’ acoustic devices, you can do a lot to improve the sound, with small changes, and for a fairly low cost, direct in the analog / acoustic domain, before eventual digital corrections. I have a pure tube music system, and to my ears, the less digital and the less s-state electronics, the better.
My two Daads do not offer a "dramatic" improvement, my room is fairly big and good-sounding anyway - it is subtle, but it is there, and this pays off, over hours of listening.
Anyway - it is fascinating how sound is an evolving revolution.