AIUI, if you have a fingerprint unlock or passcode unlock set up, when you do a factory reset the encryption keys are erased meaning that the info is still on your device but it is encrypted and the encryption keys are no longer recoverable so no one can ever access the info. If I am wrong in my understanding, please correct me. Also AIUI, if you don't have a fingerprint or passcode unlock set up and do a factory reset, the information on the device is recoverable, albeit someone would have to have specialized equipment to recover it. Again, if I am wrong in my understanding, please correct me. Thanks!