Thanks for all the reply's guys.
First off my RSI is in my right wrist and it mostly hurts with the side to side motion of a mouse.
I ended up pulling the trigger on the CST 1550 due to the low barrier of entry. My conclusion after using it for a few weeks is a really like the form factor. I will say that CST 1550 does not do diagonal motion very well (at least mine) and will occasionally catch, making it so I cant go left or right.
With those negatives out of the way I still really like the trackball. The form factor is perfect for left hand use and I have switched to using it as my primary input device at work. I still have a Logi M570 thumb ball on my right hand side for scolling and if I need to be a bit more precise but all and all I really like the CST.
In order to resolve the few issues I have with the CST 1550 I am thinking I will pick up a CST L-Track next. Hopefully the new design of the rotors will solve a lot of my problems and the inclusion of a scroll wheel will be very convenient.
I have not found a lot of conversations online evaluating the CST 1550 so hopefully this can help someone else who is in my position(considering the CST 1550). Overall I would recommend it if you can get it cheap like I did, but I will upgrading. It was a good buy in that it has converted me to CST trackballs and left hand use.
Now to find a L-Track on ebay for a decent price.