I installed v2.21 (before reading the full 66 pages of this thread) to try to fix the broken bluetooth firmware on a F9220BT.
After I read some of the warnings about v2.21 I immediately made backups of all the files and looked further for a fix for my bluetooth.
Following the instructions on this <a href="http://avic411.com/index.php?/topic/37407-2013-eu-update-f30-f930-f9310-f40-f940-f840-f8430/?hl=%20f920bt%20%20bluetooth">thread</a> the system updated successfully and I now have working bluetooth.
As others have said, v2.21 doesn't really allow you to do anything you can't
