Assassin snail efficiency?

Sorry.. wasn't sure how to phrase it.. but I'm thinking about keeping MTS in my tank, and I guess my basic plan was to order assassin snails as a back-up in case they start overpopulating (I'd only buy them if my MTS over-breed). I also was thinking about keeping a single golden apple snail in the tank (which species was it that only eats the decaying plant matter/ not live plants?) So I guess my question is this..

If I got a single assassin snail, would it completely wipe out my MTS population or only keep it under control (or would I need more??) And also.. what size would my golden apple snail need to be in order to be safe from the assassin snail (Or would the assassin snail try to harm it anyways)?

Thanks for looking!

Razzle that's plan A for me.. but I was wondering what my other options were if I couldn't keep everything under control. But yes preferably I'd like keep them under control without having to use an assasin snail. And msjinkzd, I had heard of groups of assassin snails attacking larger snails (like apples) but I was wondering if a single assassin snail would still attempt to hurt a large snail, and it's sounds like you're saying they would.. so I guess I'm just going to make sure I can keep the mts population under control before I get a pomecea diffusa. I looove those cute golden ones ^_^ Hah.. I just thought of a name for one.. the Golden Snitch . Hmm yes, I like it!

Thanks!!