Compressus is a member of the Serrasalmus genus meaning it is highly recommended to be kept as a solo fish. IMO its a very beautiful piranha. They will eat the same as most piranhas, almost any white fish meat, such as shrimp, tilapia, scallops, pellets, flakes.
As is with most piranhas they are usually very shy/skittish fish at first so dont expect it to be a monster right out of the box. They take alot of time to adjust to their new tank. Even after a long period of time it may never be an aggressive fish.
In captivity they can reach around 10" or so TL. I would suggest a minimum of a 75 gallon tank.
Hope this helps, and if you have any more ?'s feel free to ask Ill try my best to answer.