We have been looking at ways of using the feet under speakers, without raising the speaker too much or making it unstable.
We have been testing the new suspension bridge under a pair of tall horn speakers, about 40Kg in weight. the front is heavier, so the height adjust ability of the feet is really useful. They certainly reduce the vibration in the floor. At present they do bend more than is desirable, but I have a solution up my sleeve, which I think will look quite funky.