This is a great mute to fill the gap between metallic straight mutes and those designed for really soft playing. Sound is, for me, the best feature of this mute.
However, the response of the mute when playing in the low register (C and Bb trumpets) is not amazing (still good though!). I also own the large size MB mute, and that is probably the best in terms of overall balance. I suspect it is due to the different shape between the two sizes which makes the L-size respond better in the low register (perfect for things like the low F# in the trumpet part of the Shostakovich piano concerto). The L-size mute is a touch louder, and much more free blowing than this normal sized mute. Probably this normal size is best suited for D or Eb trumpets.