I put 2 those panels on the ceiling and 1 "t.akustik Print Panel The Needle" on the wall. I have 3 exactly the same rooms in the house and the room with those panels is now sounds completely differently.
Not only did the echo disappear, but even when I talk, my voice sounds slightly different, probably because of the lack of echo. I like the result so much that I am going to order more of those.
P.S. I would like to emphasis that I also used a wall panel, it boosted the effect.