I can understand this completely. They can change the sound radically, and usually for the worse. I have found that only a few of the caps work for me, and only in certain specific applications, and then only some of the time   .

The other thing, is that BG's don't seem to like metal film resistors ( and esp Vishays ). Carbon films seem to be a natural partner for them.

The gains that they bring when you are patient and get it right, can be large.

Best Regards

Dave