S!
From all the memoirs I have read about German Bf109 aces only Marseille was known to use flaps a lot in combat, very successfully that is. But he was a master handling his plane and extremely good marksman as well. Lipfert, Rall, Knoke, Hartmann and many others others never mention using them, except for landing.
Anyways using them in combat is risky if the opponent can "hide" his E-state and make you deploy them, thus bleeding your E = you are in trouble. Especially risky at low altitude where you can not regain E by diving or your aircraft is slow to accelerate vs. the opponent.