There are many differences:
Concealed command must be deployed in turn 2, and troops must respect side area interdiction. The elements, when deployed, can be put on the table as desired, for there is no need to mark the exact position. In a combined arm command this means looking for the right match up. CC is then a useful tool defender has to avoid that attackers uses fully the advantage in deploying second, throwing him off balance for 1 turns.
Ambush instead does not respect at all normal deployment rules, so you could deploy KnX in the 400 paces near side edge or, as defender, exactly at mid table. Look on the rules for the different deployment allowed. You need to mark exactly elements position, but the ambushers can stay hidden as long as they wish. Ambush is a more effective way to field your troops, but cost more and hide fewer troops.
