Currently in the final step: sudo ./flash.sh
Detected Linux
Searching device to flash..
Found device with vendor id '0fce': Bus 001 Device 023: ID 0fce:adde Sony Ericsson Mobile Communications AB C2005 (Xperia M dual) in service mode
Fastboot command: fastboot -i 0x0fce

How long is it supposed to be? (15 minutes so far)

(...) Aborted :-(
Phone still running Android.

(...) Retrying after pressing volume up a bit longer than before. Blue LED instead of green. Now flashing. Phone rebooted as SFOS (Without a SIM card, as the required size is now even smaller.)

Thanks a lot, Jakibaki!