Hey all! I just signed up today but have been following this thread for some days now.
Just to let you know that this morning I took the plunge and updated my UX250h with the stuff being talked about here. I searched using my VIN to be sure I was eligible for it.
All went buttery smooth, there was just a moment where it did seem to stall for a couple of minutes, that was at 50% of the last sub-phase (USB3, "Pre Install" phase), but then it completed succesfully and after one last autostart and some seconds I reached the final confirmation page.
Used an 8GB stick as USB1, a 256GB Kingston SD card as USB2 and a 128GB SD card as USB3, both cards used with a Lexar card reader. Everything formatted with SD Card Formatter on Windows 10.
Basically: USB1, procedure starts by itself after some seconds --> Reboot when asked WITHOUT removing the stick --> Remove USB1 when told so and insert USB2 --> Manually start the update and allow it to proceed --> Turn engine off and back on when told so --> Remove USB2 and insert USB1 again, wait several seconds (30-40) until it starts by itself --> Remove USB1 when told so, turn engine off and back on --> Insert USB3 --> Manually start the update --> This one involves several autostarts and phases, just wait --> Remove USB3 when told so --> Turn engine off and back on --> Insert USB2 --> Manually start the update --> This will update audio to the latest 1075 release --> Turn engine off, wait 1 minute, turn it on and wait 2 minutes --> Done!
I had to reconfigure settings (language, time, ...) and to recouple my phone, but link to MyLexus was kept, it wasn't necessary to reconfigure the account.
As soon as the unit succeeds in connecting to internet, you'll get a message about you having succesfully migrated to MM19.
Only thing left if you want is to update Navigation software from the installed 1120 release to the latest 1140. Has to be downloaded separately as it's not included in the packages.