Newf's photo looks like christmas tree moss lumped together. Definitely not a marimo ball which is algae and grows very slowly. I had heard that they may out compete other algae for nutrients and therefore is a good addition to a planted tank.
I had 2 and they are easy to care for, just as people described with care, any light, turn to keep round etc. They do collect mulm though and you do need to rinse them out in tank water on occasion.