They breed slowly and can't eat algae. I find that once you no longer have any 'extra' snails they prey on their own young and with giving them away/selling them to other aquarists they never get a very large population going. In any case they never bother any plants, lol. Terrific at stirring the substrate like MTS as well.
"In the land of the blind, the one-eyed man is king" Desiderius Erasmus