The Bach 5GS trombone mouthpiece is a good example of the high quality product that you would expect from Vincent Bach.
This mouthpiece is shallower than the more popular 5G and so makes the higher range a little easier and the overall sound somewhat brighter. I find that these characteristics make this mouthpiece useful for solo performances when the bigger, darker sound is not so crucial as in an orchestral or band section playing situation.
Overall, a useful mouthpiece, but not one which I would use in all performance situations.