You know, by the time the show gets around to introducing his proper suit, I found myself wanting Matt to continue on in his vigilante outfit. There is sound wisdom to Matt donning a suit with more armor than what his vigilante suit offered. However, I feel that the black suit spoke more to his character. In this show, Murdock wasn't concerned with taking on some persona, or name, or a flamboyant look. He needed his identity obscured and some protection, and he went with the most functional stuff he could get.
Honestly, I feel that the black suit looks far more imposing than the armored suit. The under-armour shirt of the black suit displays Matt's physique and lets you know that this is a man in top physical condition. The dark mask has no eye openings, which gives him this intense appearance and subtly conveys confidence. I can imagine the confusion that a criminal would have in seeing man that is blindfolded, in the dark, yet approaching with no hesitation, right into the fray of battle. Someone like that is either nuts, or highly skilled, and neither outcome would be desirable to face in a fight.