I use them for several days. My room had great need of an acoustic treatment because I had a flutter echo and reverb was a little unpleasant.
Once installed, so I replay the songs I knew and there, the sound had changed! I found a warm and dynamic sound.
Indeed, having reduced the treble, these foams have allowed the bass to be a little more present and more accurate.
The price is still high for foam, € 185 pack of 12 plates, but they are wonderfully good job.
Be careful not to abuse it because the sound reproduction may become too dull and become annoying.