I only have one flagfish.. i would get one more, but i have a small tank.. and the flagfish is meant just for maintenance. Be aware a the pair may get aggressive if they choose to spawn.
it seems that the temperament, and whether or not it tears up the plants tends to vary from fish to fish. I've kept one that is very aggressive toward my fishes and nibbled on my polysperma, but the current one is quite timid and I haven't witnessed her nibbling on any of my plants.