It advertises it as for trombone as well as trumpet and the information about it seconds this idea, which is why I ordered it, but it just isn't quite big enough in any dimension for trombone mutes. Some of my mutes don't really fit well, such as my solotone mute, and my cup mute is so big it basically removes functionality from the neighbouring holders.
This said, it has a great build quality and looks like it would be really great, just not for my personal needs.