It's not the complexity that is the problem I have with this rule, the problem is if you have played most other games you expect that when a unit has been engaged in combat, it stops moving. It's also a difficult rule to teach because its not really something you teach to a player until it comes up in a game by happenstance, at which point, it can have the feel of cheating. Again, this is because most wargamers expect that when a unit has been charged, it can no longer move. The idea that part of a unit can, in this one circumstance, act independently of the unit to my mind adds friction.
