The only benefits CST trackballs have is that they are reasonably rugged, and that it is impossible to remove the ball itself without disassembling the casing. Both are obvious benefits when it comes to users with limited motor skills.
In every other case, they're completely inferior in ergonomics. Because of the bearings, they are very much biased towards X and Y movements, diagonal movements tend to wander and feel stiffer than straight up/down or left/right. Completely inferior to a trackball with "floating" ruby bearing, like what Logitech and Kensington use.