Honestly I didn't expect much, but they were cheap and I figured they at least wouldn't make the acoustic properties of my smallish home studio any worse. In parallel with purchasing these panels, I built myself a couple of large corner basstraps using heavy rockwool, and I did quite a bit of testing to find the best placement on walls and ceiling. Combined the acoustic treatment of my studio has done wonders, and the previous nasty echoes are gone. We now use the studio for band rehearsals, recording and mixing, and the sound is a lot more balanced than it used to be. Even drum recordings sound sound pretty darn good!
One warning: They are somewhat delicate and will rip when abused!