MP3 ringtones have minimal impact on your iPhone's battery life because they are generally short-lived.
The legality of using samples of popular songs depends on copyright. It is better to choose royalty-free MP3 ringtones to avoid any legal issues.
MP3 ringtones are generally compatible with all iPhone models, but it is important to make sure the ringtone is in the correct format for your device.
The sonnerie mp3 you choose reflect your style, your mood, and sometimes even your sense of humor.