What typically happens is that you need the device reset by Superchips. If the device is within 12 months then it will be reset free of charge, otherwise i believe you have to pay around £200 to have it reset.
Once it is reset you can then use the device like a brand new item. You will then need to plug the device in to download your cars stock ECU configuration. You then send this to Superchips, they provide you with an upgraded map as well as storing your stock ECU map in case the device ever failed. You can then plug the device in and switch between stock and upgraded.
If the device is not reset then the maps are specific to your friends car.
Hope that answers your question.