I didn't try the trackballs that you use your fingers with. The thumb-controlled ones are pretty natural to use, as the left and right click actions and the scroll-wheel are identical to a regular mouse. I suspect the act of using the same finger for moving the ball and clicking the button would be more difficult (at least for me :) )

I haven't used a mouse in years, just Kensington trackballs and laptop trackpads. The trackballs are great; clicking is predominately with the thumb whereas pointing is with the fingers. Even when using fingers for both, it's not something I notice since I've never clicked and moved at the same time - maybe for a gamer it would be different

I also have a kensington, and it’s easy to hold down the left click and move around the cursor.