Most of people think that all the data can be erased completed from iPhone after factory reset. Actually, the erased data can be recovered with recovery apps.
To protect your privacy, you need Dr.Fone for iOS. It removes your personal information permanently. Nothing can be found after removing even with recovery apps.
It is wise of you if you have been aware of the importance of deleting iPhone data before selling [wipe-iphone.com], recycling or giving it to any one. Here this iPhone Data Eraser [wipe-iphone.com] is my first recommendation. By operating it, you can choose the security level to delete data from iPhone according to your own needs.