Hi, Howie -- I have 12 ASC sound panels, and I think they're great; they've improved a bright, echoey room without making it too "dead." They're easy to use (light enough to hang on a small nail) and to move around.
I think they do do something to the sound that is not entirely good, reminds me of Sonex in that there is a subtle but noticeable change to the quality of the sound; it was not without trying, as I had 4 panels to play with, never did find any combination that I preferred to no panels. I do, however, like the ASC Tube Traps, but not in the corners. I also had good results with Corner Tunes.
I have the flutter stix (which is now a specialty item). Expensive, but they helped tame about 80-90% of the slap echo in my room without killing off the sound.
Don't expect any effect in the bass region; it did improve in regard to clarity of voices & instruments in my tiny room.
Of course, YMMV.
It depends entirely on what you're trying to do in the room. The sound panels are spot absorbers with an absorption frequency range as specified on the ASC website. They won't substitute for bass traps in the corners, won't diffuse in areas where you need diffusion, but will absorb in places where you need additional absorption or have opposite wall reflections to tame. Typical uses are at the back of the room or near the ceiling in high-ceiling rooms. Usually they are used in conjuction with standard tube traps. In general, you should explore the room first and find out where its problems are before investing in specific treatments (reverberation, flutter echo, opposite reflecting walls or floors or ceilings, sound leaking into long hallways etc). Also furniture, curtains, rugs, and bookcases can do part of the same job.