I have several of these and i'll start by saying that overall i really like them. They have a sort of cute personality all their own, almost more like an animal than a plant because they do tend roll around and do their own thing and don't always stay right where you place them. People who look into my tank always want to know about the "tribbles". I originally bought 2 and split one into 2 so i had 3 total (i have a thing against even numbers lol), but i suppose either becuase i don't have a lot of light or because i did it when they were too small, they didn't really like that and didn't heal back up into a ball. I've since read that you should wait until they are really large and hollow inside to split them.
I just bought 2 more and threw out the one i ruined, the other half i sort of spread out on some driftwood, not sure how it will take to that. They do seem to not mind the lower lighting levels in my tank but if they are growing at all i can't tell. They are mulm magnets and need to squeezed out like a filter sponge when you do your water change and make sure they get turned so the same side is not always facing the light, otherwise the dark side will turn brown and die off.
As far as their supposed benefits regarding algae or nitrates, i have a hard time beleiving that such a slow-growing plant could have much effect.