My 2cents, whatever they're worth.
Specialized tools like this can be employed, but their employment is far more limited and in this case the consequences of using them are pretty harsh. You phoenix eye fist someone in the eye - they're not likely to be coming back for more. Chances are you will burst the eye, and in the old days that was usually the end for your opponent. If the shock didn't kill him, the likely infection probably would.
IMO specialized fist employment (to reduce risk of damaging your own weapons) typically comes after a certain degree of control is gained - you most likely wouldn't use them in free striking engagement.
In regards as to what phoenix eyes do to the ribs, it's more than just jacking one intercostal - they can break ribs and sublux others simultaneously if the right amount of torque is applied (I had a sihing who did this to someone is a self defense situation) basically shutting down the ability of the side of the body to respond in a normal matter. Someone who has some decent muscle mass in the rib area can shrug off a solid punch - there's no shrugging the phoenix eye off, it's too sharp.