Ive been using one for a week or so now. Previous trackball was a CST.
It's... okay. Part of this is personal preference, part of this is quality.
Personal preference: I prefer the larger diameter ball of the CST, as well as the flatter and more centrally located ball. I found this gave me better fine-grained control of the cursor (especially the larger ball, which gave better leverage).
Edit: I've just identified another advantage to the CST design. The large buttons on either side of the trackball are actuated by the same fingers as used to operate the large ball. On the Elecom design, the primary mouse button can only be thumb-actuated. I am finding that when I press the thumb button, my fingers remain close enough to the ball surface that I often bump the ball and move the cursor when I click. Whether this happens is going to be down to the user, but I've been using this thing for over two weeks now and haven't managed to adapt.
Quality: The microswitches in the Huge seem to use different types. Standard mouse-like (clicky) under most buttons, but the Forward/Back, Fn1/Fn2 buttons seem to use a different switch- these 'mush' when actuated instead of properly clicking. This renders them... well, close to useless for me. I had wanted to remap one of the buttons closer to the ball into the left click button, but the mushy buttons are not viable as a primary mouse button.
This brings me onto the next quality issue- the software is utter garbage. It doesn't write into the trackball firmware, you need to have it running all the time if you want to remap buttons. If you move the trackball across multiple machines, you need to install the Elecom software on each machine. I've had it default into Japanese, and had to guess around to change it back to English. And most of it is comprehensible once in the language of your choice, but at least one of the functions was described so obscurely I had to Google it.
I do have replacement ceramic bearings making their way slowly to me, which will be swapped in out of curiosity. But the ball and smoothness are not problematic (as others have been having issues with).
Overall: It's usable (barely). It's cheap. It's nowhere comparable to a CST- it's big but flimsy, it's got some major UX issues. If I were based in the States, where I ordered this from, I would be returning this. Unfortunately, return shipping would cost about as much as the trackball.