I've kept a school of these fish for a couple years. Despite being said to be fin nippers, i find when you keep 2 females to 1 female they will keep the aggression to their species only. The males do have mock fights which are fun to watch. They keep to the middle of the tank, rarely ever going towards the lower or upper regions. They school rather tightly unless they are in the mood to breed, then they stake out their territory and guard it.
these tetra are brilliant for many reasons one is that they are great at dealing with aggression, they can compete with cichlids, tiger barbs and even blue crayfish (although i had one casualty). It was a mistake with the crayfish but they are survivors, eventually they will learn their aggressors ability and simply out swim them. Watching 4 diving through the snipping pincers of a crayfish to steal food from its incisors is nature in the home. They are very clever and aggressive themselves one female used to swoop under my catfish and bite off his whisker and once they learn a betta swims like a worm he will be dead in a few days. but overall these are great fish that love to compete with each other and will keep the edge up in any small tank. I only have three but they do not seem effected by this and continually try to dominate each other.
I really like these fish. They are a quite active fish and are always doing something. I've found that both males and females will spar and display towards each other. Males have great coloration and finnage, and the females do as well--I've had a few that had the most beautiful red finnage. I've had no trouble with them as fin nippers, and they seem to mind their own business, that is they only bug their own species. My only complaint with them is that I can't keep them alive for more than 6 months. I've had a school of 10 neons for over 1 year now, and only 1 fatality. I've had at least 10 (lost count) black phantoms over the same timeframe and in the same tank, and I only have 1 male left. Not sure why. If I could keep them alive I would have a school of 10 of these guys easily.
Gotta say, I loved the look of them but wasnt happy when I got them home. After a few weeks the males bullied each other so bad that the scrawnier of the bunch were nipped to death. More aggressive toward each other than rainbow shark in my opinion. Although, now that I only have 3 left it has calmed down. I don't see them much in my heavy vegetation.