Amano shrimp are cool, they dont prey on fish, they do eat them when they are dying or on their last fins(get it??) but thats a good thing as it stops disease in the tank etc. Shrimp eat anything they are the bottom feeders, fish waste excess food and best of all algae!!!! they are mini walking filters- you have to have them- and like someone said they are part of the fun- just as fun to watch as the fish but not as pretty!
They shed their shells when they grow, however they can shed shell and become smaller if there is a lack of food resource.
One shrimp not to get is the glass shrimp it grows to a large size and will eat your adult cardinals!
Oh one more thing you cant keep shrimp with angels they find them tastey- your safe with most fish but stay away from large tetras, and something a bit frisky llike the loach family.