I bought the Wallace cup mute a few years ago after many recommendations from fellow trombone players. After years of surviving with cheaper cups and their different problems, this one has proved to be really worthy also in professional use. The cup is adjustable but not loose, which makes a big difference if one wants to use the same cup with different instruments (=varying bell "depth"). The materials and build are suitably sturdy, I've had nothing to complain about.
At least for me, this cup mute has also been the easiest to play with by far. It also looks awesome!