Apple snails lay their eggs above the waterline and so are not like pest snails as the eggs are easy to remove. They won't hatch underwater. I'm thinking of getting a group of apples soon but i'll get a few different colours for variety. Take a look at this link http/www.snailshop.co.uk/ to see some gorgous snails.
I made the "mistake" of letting a clutch hatch one time. It was almost creepy -- tons of ivory-colored snails EVERYWHERE, on everything in the tank! Kinda cute as they get bigger though.
But as long as you remove the clutches before they hatch, you'll be absolutely fine. Apple Snails are lovely little things.