Fast contact backup is an application to backup your contacts of iPhone on your email. So You don't need to use a Computer to back up/Restore contact.
You Just need to take backup contacts using application send email you your self and later on restore contacts.
InApp Purchase Details :
This InApp Purchase offers a Life-time purchase. Unless you cancell it. The InApp Purchase fee is charged to your iTunes account at confirmation of purchase. You may manage your InApp Purchase and turn it off by going to your settings.
Terms & Conditions : https://docs.google.com/document/d/1wFHD14RFxCjqgRH5wx8MyjRNtG4uimMV18aIp8xYhUk/edit?usp=sharing