"happy to assist"
Happy to assist, doing what?
Opening the exit(s)? Were you shown how?
Restraining over zealous pax?
As crew are in uniform, they are easily identified by passengers, and are more likely to be taken notice of by passengers during an emergency, than by someone indistinguishable from the rest of the melee.
So perhaps our "designated helpers" in these emergency rows, should be given more comprehensive briefings, and there should be quick don, high visibilty vests stored either in the o'head locker, or under their seats, that make them readily identifiable as an asistant.
In my opinion, I believe there's only lip service given to this Civil Aviation Authority requirement (of every country) of airlines to allocate certain people (and deny others) to emergency exit row seats, at this point in time.