There is a noticeable difference when using them with large power tubes (2A3/300B/etc), especially when direct-wired in SET configurations. The larger the tube, the more difference they make, in my experience. Whether or not you like that difference is obviously a matter of personal preference.
If you doubt the effect, put one around a slightly microphonic 6922 and listen to what happens. Hocus pocus, my hiney.
If you doubt the effect, put one around a slightly microphonic 6922 and listen to what happens. Hocus pocus, my hiney.