I got a set of these things in a pile of old stereo gear given to me. Just before I threw them away, I thought what the heck. I brought them into the stereo room and placed them one each on my tube monoblock amps.
I listened for about an hour. Took them out for about 5 minutes, then put them back in. They are never coming back out
I could not believe how much better my system sounded. Especially, the separation between instruments and voices.
I am a firm believer!