Originally Posted by iBok

Both M11 and M11X have the same 4th channel that can only be used for brake mixing

other M11X features:
user customizable menu for commonly used features
failsafe (also on the DSSS and FHSS-2 versions of the old M11)
FHSS-3 technology, also compatible with FHSS-2 receivers
uses 6 AA cells instead of 8
127g lighter