Nice setup ! As phones are cheaper and cheaper, they are a lot of useless phone, this give them a second life !
But be carefull with the antenna, must be removed to be sure.

Also, QR code transfert are really good, because there is few information, so you will be 100% sure it's legit way to communicate between devices. If you use USB on a computer there is a lot more "memory" available so a virus can possibily steal your coins... QR code tfw