So not true, flowerhorns can be socialized! I know of plenty that have worked. I own one, Prime is so laid back and relaxed it is funny. Long as you dont mess with his food, he's good.
id have to say biggest ive seen was about 15" so yes they are monster fish when they get to that size, as well as their aggression towards anything that moves. and you can keep flowerhorns together only for a short period of time. out of experience, you are bound to loose 1 or 2 if you have it in groups. another way you can pull it off is have a very enormous tank. as long as they have their own territory and enough space to move around they wont be as aggressive.