They have pins longer than 5", or possibly real high or real low top weight.  That may limit your drilling options, or it may not depending on what layout you want to use.

"Pro pin" is really just a way of dressing up a second quality ball (a "blem") and getting some money out of a manufacturing defect.  They are legal for competition, and they have the same core and cover as first quality balls.  Some companies use them for their ball staffs because professional-level bowlers can usually make the ball do anything they want anyway, so having weird starting specs isn't much of a hindrance to them making the ball look good.

SH