they generally peaceful, but DEFINITELY a predator. Not sure why anybody would say they are not a predator. Mine eats large smelt and prawns. LOVES it if I throw some insects in there or feeders. Very nice color. Can be quarrelesome sometimes, but no real damage done. Mine will mix it up fighting with both my dorado and atf (both of which are larger). It would be best to have at least 5 of them. They will quarrel a bit, but they also seem to like to "hang" together when not fighting. They should have a pretty large tank, not because they are active, but because the swim VERY fast and are skittish sometimes (though mine is not very skittish at all?)
Get VERY nice coloration as the get larger. Yeah, 8" seems to be the norm. I have seen them over 10" in a friends tank, but that is unusual.
I am not sure about the jardini eating them (mine is in with a 2ft arro), but because jardinis are so mean, you run the risk of the jardini murdering these guys.
In all, a great fish, beautiful, and under-appreciated. They are heavy and sturdy fish, have BEAUTIFUL deep red tail and bright yellow fins when water conditions are good.