Owners are not complaining about the performance of the key action.

A post from Facebook : I've found the non-weighted Casio keys to be notoriously inconsistent. Sometimes you get one that's quiet...sometimes it's noisy. The culprit is inconsistent application of the grease they use to lubricate the keys. That grease keeps the plastic pieces from clicking when they, inevitably, touch. You see, the entire key mechanism has no springs, and the keys are manufactured in strips (rather than individually). The only thing keeping keys in place are plastic slots they fit into. This is very different from the standard Fatar keyboard that keeps each key individually placed with a spring and, often, felt. Casio's keys are cheap to manufacture and, consequently, are one of the things that keep their costs down....which is entirely appropriate for their consumer-grade keyboards but, as you point out, NOT the greatest decision for their pro gear.