I am using resonators since quite a while. Frank Tchang, a French manufacturer of the Acoustic System resonators, put them on the market some 10 years ago. While I am not using too many room tuning tools these small metal sound bowls are really improving the audio sound you hear in your listening room.
Two silver bowls on the front and rear side, as well as two copper bowls on the left and right sidewalls do have quite some effect.
Tchang writes on his side : The miniature wings on the bowls are directional and asymmetric in their attachment to offer large and small windows. The resonators attach to walls, furniture or fixtures in or out of sight with removable BluTack. Precise location and wing orientation provide unlimited tuning options to help defuse air compression zones and shift specific sonic aspects. But the resonators improve not only the sound. They also help to rebalance the energy flow, reduce the background noise and improve the serenity of an enclosed space. Resonators are used in yoga, meditation and wellness centers where no music is played but the goal is peacefulness and regeneration.
Okay, you need testing it out. It is not voodo, as most of the room tuning measurements are. I know there are many non-believers regarding resonators, you just have to experience by yourself.