TuneClone is developed to solve this problem exactly. It can convert the purchased iTunes music collections to general MP3 files.
M4P music files can be played on Apple products only, such as iPod, iPad, iPhone, iTunes, etc. In order to enjoy music on other common used devices, TuneClone is designed to release the limitation of M4P music. It's very convenient to use. Just download and install TuneClone, and then M4P can be converted to mp3 with several steps.