I am a professional pianist and play a variety of Steinway, Yamaha, Baldwin and Mason & Hamlin pianos and Roland, Yamaha and Casio digital pianos on a daily basis . I have owned the the older FP-4 model for years and have recently purchased the newer FP-4F model. The piano sampling is improved with a better longer sustain, more legato response, a darker and fatter tone, and more it seems more natural or "organic" sounding.... however the new FP-4F's action is very disappointing. It's sluggish and physically tiring to play. I can play Chopin Etudes on the old FP4 action with out straining but I become quickly tired on the over weighted new FP-4 action. It is a strain to play it for more than a few minutes. My wrist tendinitis came back after playing the FP-4F action for a for a few minutes. It feels stiff and resistant, the keys don't bounce back or move as fast as the easier to play FP-4 original action or as on my Mason & Hamlin grand or any of the acoustic piano I usually I play for that matter.
Two other complaints I have are that they have not included an editable Effects generator on the new FP-4F, whereas the old FP-4 had a sophisticated library of effects. Also, there is no volume balance control for when in Split Mode, so if the bass for the left hand is too loud or too soft for whatever sound you are using in right hand you are stuck because there is absolutely now way to adjust the balance.