S/Lab is Salomon's race line and the Phantasm is the road end of it. A full-length carbon plate runs through a PEBA-based foam under a 39 mm heel, and Salomon developed the shape with the aerodynamics people at Swiss Side, which tells you what kind of margins it is chasing.
It suits you if you race on road from 10K up and want a plated shoe that stays light rather than tall and soft. The plate argues back at race effort and does nothing at jog pace, so it earns its place on race day and the sharpening sessions either side.
It is not a trainer. There is not much shoe here to begin with, the foam is expensive and short-lived, and the price only makes sense if you actually pin a number on. For anything off-road this is the wrong half of the range entirely.