I just installed a left hand Throttle Rocker this weekend. I have used a Throttle Rocker on the throttle hand for a while and have found it to provide a little more comfort, especially in city riding. It takes a little of the pressure off of your wrists and hands. I bought the left hand model with the hopes that it would do the same for my left hand, which after installing the original throttle rocker was now the only hand that ever bothered me from time to time. Well, I have to say that I am not disappointed! I rode about 75 miles today in city and highway traffic and had no discomfort at all in my left hand.
Try one before you spend a lot of money on bar backs or other bar modifications.