Standard valves crack with age and heat cycling, and rely on rubber diaphragms which perish. They're also simply not designed to handle increased boost levels. Its billet aluminium construction provides strength, while the precision-machined lightweight piston gives excellent valve response and sealing without relying on rubber diaphragms or O-rings, so it's far more durable, and guards against compressor surge even when the boost is turned up.
Moderate sound volume, neither too loud nor too small.
Easy mounting.
Durability will be known over time, but it is so famous.
However, there is no detailed description of the upper valve softer and harder.