I agree with Bit,
It's pretty easy to figure out what frequencies will be "treated" by various materials.
Almost none of the materials sold and used for room treatment will absorb the most problematic frequency resonance in a small or medium size room.
All they absorb are the mids and higher frequencies, which makes it easy for you to hear that you have made a change... the curious thing is that the change you are making is not helping tame any of the problematic resonant frequencies in the room, you are simply EQ'ing your wonderful voice in some arbitrary and novel way.
If doing that makes you think you sound better...
who can argue?
If the Reflexion devices came with mirrors attached... I think they would sell even more of them.
There will be, however, the matter of those problem frequencies that still need to be dealt with.
You can hear the room tone in the intro to the video where Monique is singing and the camera mic is picking it up. It is the low frequency echo you hear under the entire interview. You can also hear that she has a wonderful and beautiful voice.
Close mic'ing and low cut filtering are probably all she needs to sound good. She even mentioned that sometimes the practice tracks make it to final mix... more proof that her voice is simply that nice to work with. :-)
best regards,
mike