Like any other mechanical or elastic device, the Pojie's properties are subject to fatigue with repeated use and intensity of use, just like your strings. For example, there may be a difference in the life of the Pojie for an aggressive baseliner who knocks the cover off the ball compared to a steady grinder who relies on touch and placement.
Ideally, for optimal performance, you would replace your Pojie each time you restring your racquet. There is no easier way to improve your racquet's performance and comfort than by replacing the Pojie (and strings) with a new set.
However, the Pojie is engineered not to wear out with average player use through 2–3 stringings. When you begin to notice that the performance and comfort properties of the Pojie have diminished, then it's time replace them. You can also have your stringer examine the Pojie string guide and compression core for wear.