I have some in mine and find them very beneficial. They dig through the substrate and eat the detritus and decaying plant matter aswell as un eaten food. Like as stated above they won't get out of control if there is not an excess amount of food for them. Oh they are also nocturnal so you shouldn't see them often. They are especially useful if you have sand substrate as they keep the sand stirred up and prevent toxic anaerobic pockets from forming. If you have a planted tank you don't have to worry about them eating your healthy plants then will only eat the decaying leaves and such.