I don't know if Noisy still cares about this, but I have finally received my replacement PCBs and constructed this trackball. Here is my initial impression:
Assembly is rather straightforward. Just make sure to actually follow the instructions! There are some quirks to figure out when assembling the shell.
The shape is very ergonomic, but it's hard for me to keep my hand planted on anything. I have a tendency to hover my hand above it and rest only my wrist on it; that's just the way I am. If my hand is planted, the trackball is reachable only by my index finger, but I prefer using my index, middle, and ring fingers together to move the ball, which is easier with a floating hand.
The buttons all click nicely, provided you assemble it correctly. It's very touchy about slight differences in angles when screwing in the buttons and the top and bottom shells, so once you get it put together with everything working, just don't mess with it again. The hardest part to get working well is the scroll wheel. It will get stuck if things haven't been put together "just so". There is a 1-1.5mm gap between the right-click button and the upper shell, but this is purely cosmetic.
The ball itself is rather rough. I've read it smooths out over time, which I hope is true. When brand new, it's not very pleasant, but it is accurate.
I haven't tried reprogramming it, so I can't provide any feedback on that. Thus, my left and right click buttons are on the left side.
Two improvements the user could make to this are adding some kind of weight inside the shell and/or replacing the included cork feet with rubber feet in order to prevent its slipping around the desk, which is a slight problem given the left click button presses in from the side.
Overall, CST vs. Ploopy: CST's ball is way smoother, but Ploopy's ergonomics are way better.
So far, I like it!