HefnyCopter Firmware works in KKv2.1 as in the demo
can switch between X-Mode & Plus-Mode.
there is also HefnyCopter2 that works on KK2 it has more new features:
1- BuddyMode where u can train ur friend using another 2 TX at a time.
2- XBEE connection where u can connect your quad to PC.
HefnyCopter is released wheile HefnyCopter is still in final developing phase :)