Warm and open, while still retaining that quintessential 'cup mute' sound. It certainly has all the notes, too!
I have every Bass Trombone mute from MorningStar mutes. Each is impeccable in quality, and sound, as well as build, has great intonation, and does not make my horns play sharp. I consider they used to be master-crafted mutes, and well worth the price paid.