I don't know if T mobile demos exist, but I had a brand new Verizon demo I got on eBay for $60. It was running the demo software, stopping it from charging past 50% battery. It also came with a retail mode app that put some Verizon promo on it every time you turned it off, but I was able to remove that by using ADB AppControl. Earlier in October, someone confirmed that the South African kdz basically returned the phone back to stock, but since it physically didn't have a cellular modem or fingerprint sensor, those things wouldn't work. WiFi, however, did work. I just flashed the South African kdz though LGUP while my phone was in download mode. I also just received my fingerprint sensor I got off of AliExpress and put it in and now the fingerprint sensor works as well.(I have some other phones so I don't need this to have working cell service) Through TWRP, I was able to root and flash a custom kernel someone made here on xda as well. I did madke a QFIL backup of my device although I doubt I'll really need that.