The Harimoto is pretty much a drop-in upgrade for Korbel Japan. Touch game is nearly identical, and the transition to carbon kick when speed goes up is very gradual/natural.
Viscaria is a more sharp experience. If you like Korbel for its capacity to hold the ball quite long, you will find Viscaria a big change. Besides that, the carbon kicks in pretty quick but that also makes it more predictable. Works better with compact strokes (compared to Korbel/Harimoto).
The Freitas, I can't tell you anything about personally. But there's reviews all over the place.