This is the only trombone straight mute I'll ever buy. It works, price is nice, and is light enough to manage to put it in my bell in 2 measures time with some songs.
If you have a nice trombone, don't stuff this in the bell to fast, as it leaves some marks on the outside of the bell because the materials this thing is made of are obviously stronger than a trombone.
Will buy again if I run over mine with a tractor accidentally.