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 ftw

Yes...not all antennas are easily removed. The first cheap phone lg i bought..even the phone professional didnt want to try.
Then i found this model. https://youtu.be/ICV7vPF9mPE
As soon as you remove the battery...the antenna is there...5 screws and its out!