They're super easy to take care of and very cute. I saw them at Petsmart and I was like, "What is that? Marimo ball, what is that?"
So I did a little bit of research and learned they're a nice addition to a tank and very easy to care for. Just gently squeeze them and wash them in cold tap water. Then you can plop them in your tank. They can float for awhile because they're full of air but they'll sink.