Would'nt be no expert but i know they'll help keep any algae at bay as they're a form of algae and out compete other algae for nutrients. Look good too.
Although mine never seem to grow in balls. I think my tetras pick them to pieces and they then get tangled with the java moss, which makes one hell of a mess.
Don't expect them to help in terms of fighting algae in the aquarium. Algae need very little in terms of nutrients, CO2 etc. You'll never beat it by limiting these.
Good read
http/www.ukaps.org/forum/viewtopic.php?f=21&t=16920&p=174454&hilit=compete#p174454