Conn 4M New Wonder "series II" Curved Soprano
Date: 1924. Image by VintageSax
This is a curved soprano saxophone in Bb (and not an alto saxophone). All "New Wonder" saxophones have rolled-tone-holes and "nail-file" G# keys. These days the community calls these the "New Wonder (series) I" or "New Wonder (series) II" saxophones. Conn themselves never referred to these as "New Wonder I" or "New Wonder II" but simply as "New Wonder".
In the following I am assuming that Conn's curved soprano's are basically of the same design as the straight soprano's, and that whatever applies to the 18M will apply equally to the 4M. For a thorough review of the 18M New Wonder "series II" straight soprano saxophone, see Thomas Zinnen's discussion here.
In his review, Thomas Zinnen says the sound of the 18M straight soprano saxophone is "awesome". However, because saxophones built in that era had a different design to modern ones, it absolutely requires a vintage mouthpiece. A modern mouthpiece will not work properly and cause the instrument to be out of tune with itself. Judging by the review, you will have to experiment with mouthpieces until you will find one that works. With my admittedly meager knowledge of saxophones I seem to remember reading somewhere that in those days saxophones were built to take mouthpieces with large chambers, much larger than most modern mouthpieces. That might be an avenue to investigate.
Thomas Zinnen says the keywork doesn't feel very ergonomic and perhaps was designed for someone with small hands. It doesn't have a high F# and no left hand G# to C#/B/Bb activation. Thomas also strongly suggests using a good saxophone technician who knows what he or she is doing with respect to this kind of vintage equipment.