Definately stowaways. Thought i'd leave them, not realising the amount i'd end up with. I'm personally not too bothered about keeping the pet snails, even if they look quite interesting.
I think ultimately my best method of removing them is going to be one of predation, I don't want to add any more chemicals to my tank than i have to. A clown loach would fit the bill and they look quite cool anyway. But with one in my tank, i don't think i would have enough space to replace the platys that i've lost. Plus it would probably want to occupy the same space that my female cichlids do at the bottom of the tank, under my bogwood. I think the loach would come off worse!