In military encounters, many rules of normal interactions are void. An example of this is truthfulness. If your enemy is trying to attack you at all costs, putting materials and personnel at risk for the sake of being honest is a dangerous decision. Therefore, it is permissible to lie in such encounters.
There is no question in my mind that perfidy is a good military tactic. There is no honor in times of war. Although perfidy is considered and constitutes a breach of the laws of war but in my opinion there should be no laws when it comes to war because the men and women out there risking their lives have to do whatever it takes to make it home to their families.
At the end of the day, we have to hope our armed forces and those of other nations conduct themselves according to international humane law. That being said, if you are in the middle of a war, it's quite possible that the enemy, whomever it may be, is not going to do the same. Perfidy if it follows relevant provisions of IHL is a legitimate tactic.
Deception is dirty. Deceitfulness and trustworthiness is immoral and, in my eyes, unacceptable. However, up to a certain point, it can be used. It's up to the aggressor, however, to make sure that they do not cross the line, meaning that they won't hurt or scar someone emotionally or physically.