When you're trading off of CA3, no, because 9 times out of 10, they'll just rush you after that and since you're tagged, you're probably going to lose the fight.
Also need to take into account how few people are running explosive weapons, excluding nades, flak is just too situational. You're not going to take it to counter that one guy with an osmaw. At least talking from a fight club perspective here.
tl;dr, flak is good, just not good enough.