The only purpose of the verticle one is to keep the tail away from the ground.
Actually he is right, they did not design it do do anything other then that, with gyros today the heli will fly the same with or without a fin in fast forward flight. The fins on a model do nothing in FF, although theoretically they should but they dont, take your fins all off fly, then out them back on, you wont notice a difference except the balance will be off.
Colin