I have had two, one C* for tenor and a D for Alto.
The Chamber is round and the throat is D shaped like in the Soloist....in fact, it is my opinion that a Metal Jazz is nothing else than a Metal Soloist (and like this one older models are short shank and newer are long shank, there have been complaints in the use of older types on modern saxophones and otherwise).
It has a nice projective sound and, compared to most metal pieces is very wide and substantial. Definitely a lead instrument mouthpiece. I didn't have very good results with the tenor C*(maybe a larger opening would have improved something but the piece, as it is built, is very resistive).
If you like the Selmer Soloist pieces, this is your piece, very expensive new they can be very cheap second hand, shop around, there are many out there unloved and unsold.