A20 is the only one I see with that special thicker tip rail and whether you're a trumpet player or saxophonist

The difference between the A20 and the A25 is the tip rail is thicker on the A20 for a pure immediate vibration

The A25 is a standard V5 tip rail and is basically the A15 with a more open tip

The A20 has that special tip rail that creates that "compact centered sound" for the serious classical player