Buy more snails to take care of a snail problem?
Unless they end up killing eachother until only one remains...highlander style...I don't see the point. Getting loaches would be a better solution imho. I'm not planted tank keeper and never experienced a Malaysian Snail infestation (just a pond snail one, but the loaches and fish keep it restricted to the overflows and sump) so I'm not one to say if it's useless, I just don't see how adding more snails (even if they kill the problem snails) solves the problem.
Do those snails really work? How do you get rid of them/do they cause an infestation as well?