I haven't had an issue yet. I know there are a lot under the substrate because if I watch closely I can see it moving. There will usually be three or four out on plants eating the algae off the leaves (they only eat the dead leaves or rotting stems, they leave the healthy part of the plant alone.) Or wandering around cleaning the rocks and the log, even the substrate.
I've read that they will only multiply up to the amount the tank can support, once the supply of food is diminished, the snails will stop reproducing, supply and demand in nature is very common. But I've also read were people have stated their tanks are "overrun" with them. I don't know what they mean by overrun, perhaps they have an algae problem and that's the reason.
Anyway, I like them and don't mind seeing them in the tank, they're fun to watch and they keep my betta entertained also, he watches them but doesn't try to eat them.
But if you do find you end up with too many there are several options I've read. You can get a Assassin snail, they will eat the MTS, but you may end up with no MTS at all, then you have to find something else for the assassin snail to eat. Or they say you can just cook them, like you would a lobster, then throw them away. You can also buy a spice called Alum. You mix 3 tbls Alum per gallon of water, let it sit over night and drop in the snails, this is suppose to kill them instantly. You can also use this mixture to "clean" your plants to make sure you have no hitchhikers when you bring home your plants. When using the Alum for this purpose, keep the plants in the water mixture for three hours as it will take that long to penetrate and kill the eggs. MTS are live bearers, not egg bearers but this will kill any other types of snails that may be on your plants. They also say you can just quickly and humanely "smash" them with a hammer, then feed them to your fish...sushi! Lol
I haven't had to "dispose" of any yet so I haven't attempted any of these options. Like I said, I put them I my tank intentionally due to the sand substrate and trying to have a "natural" tank with live plants etc. But I have heard that once have you them, you pretty much have them, it is very difficult to completely eradicate them once they are in your tank without breaking down the whole thing and doing a through cleaning with salt water and or bleach.