This mute gives a good sound but does not fit very well
It is a very strange design. You have to push it into the bell very hard so you not loose it. A soft bell will be dented from the inside by the corks. When it is pushed in the sound and the respone are good.
It was first when I pulled out my Conn 73H which is a small bass trombone that I found a bell that liked this mute.